diff --git a/benchmarks/inc/utility.hpp b/benchmarks/inc/utility.hpp
index a27e1bacea..e407e2654c 100644
--- a/benchmarks/inc/utility.hpp
+++ b/benchmarks/inc/utility.hpp
@@ -4,9 +4,9 @@
 #pragma once
 
 #include <algorithm>
+#include <cstddef>
+#include <cstdint>
 #include <random>
-#include <stddef.h>
-#include <stdint.h>
 #include <vector>
 
 #include <xoshiro.hpp>
diff --git a/benchmarks/src/std_copy.cpp b/benchmarks/src/std_copy.cpp
index a84d58d19d..4cb80016f5 100644
--- a/benchmarks/src/std_copy.cpp
+++ b/benchmarks/src/std_copy.cpp
@@ -3,8 +3,8 @@
 
 #include <algorithm>
 #include <benchmark/benchmark.h>
-#include <stddef.h>
-#include <string.h>
+#include <cstddef>
+#include <cstring>
 #include <type_traits>
 #include <vector>
 
diff --git a/stl/src/vector_algorithms.cpp b/stl/src/vector_algorithms.cpp
index 5214349b76..507a0fa854 100644
--- a/stl/src/vector_algorithms.cpp
+++ b/stl/src/vector_algorithms.cpp
@@ -12,11 +12,11 @@
 
 #if (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_ARM64EC)
 
+#include <cstdint>
 #include <emmintrin.h>
 #include <immintrin.h>
 #include <intrin0.h>
 #include <isa_availability.h>
-#include <stdint.h>
 
 extern "C" long __isa_enabled;
 
diff --git a/stl/src/xonce2.cpp b/stl/src/xonce2.cpp
index a94fbaddc2..17c9a3c3a7 100644
--- a/stl/src/xonce2.cpp
+++ b/stl/src/xonce2.cpp
@@ -3,7 +3,7 @@
 
 #include <yvals_core.h>
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <synchapi.h>
 
 // This must be as small as possible, because its contents are
diff --git a/stl/src/xxxprec.hpp b/stl/src/xxxprec.hpp
index 0d9d30cfef..dc3a4491b4 100644
--- a/stl/src/xxxprec.hpp
+++ b/stl/src/xxxprec.hpp
@@ -27,7 +27,7 @@ _EXTERN_C
     } // STET
 
 #if 0
-#include <stdio.h>
+#include <cstdio>
 
 static void printit(const char* s, FTYPE* p, int n) { // print xp array
     int i;
diff --git a/tests/std/include/constexpr_char_traits.hpp b/tests/std/include/constexpr_char_traits.hpp
index 26ec4fc86e..bb53fbf6a3 100644
--- a/tests/std/include/constexpr_char_traits.hpp
+++ b/tests/std/include/constexpr_char_traits.hpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #pragma once
-#include <stdio.h>
-#include <wchar.h>
+#include <cstdio>
+#include <cwchar>
 
 struct constexpr_char_traits {
     typedef char char_type;
diff --git a/tests/std/include/fenv_prefix.hpp b/tests/std/include/fenv_prefix.hpp
index 5b768e8317..642e44a01b 100644
--- a/tests/std/include/fenv_prefix.hpp
+++ b/tests/std/include/fenv_prefix.hpp
@@ -40,7 +40,7 @@
 #endif // defined(FP_CONTRACT_MODE)
 
 #include <cassert>
-#include <float.h>
+#include <cfloat>
 
 struct fenv_initializer_t {
     fenv_initializer_t() {
diff --git a/tests/std/include/floating_point_test_cases.hpp b/tests/std/include/floating_point_test_cases.hpp
index d463fb8f3f..20fb51551e 100644
--- a/tests/std/include/floating_point_test_cases.hpp
+++ b/tests/std/include/floating_point_test_cases.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include <stdint.h>
+#include <cstdint>
 #include <utility>
 
 constexpr std::pair<const char*, uint64_t> floating_point_test_cases_double[] = {
diff --git a/tests/std/include/instantiate_algorithms.hpp b/tests/std/include/instantiate_algorithms.hpp
index 044d6ce00a..ae35649478 100644
--- a/tests/std/include/instantiate_algorithms.hpp
+++ b/tests/std/include/instantiate_algorithms.hpp
@@ -6,13 +6,13 @@
 // Notably, all permutations of all iterator strengths are tested.
 
 #include <algorithm>
+#include <cstddef>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <numeric>
-#include <stddef.h>
 #include <type_traits>
 
 #if _HAS_CXX17 && !defined(_M_CEE)
diff --git a/tests/std/include/new_counter.hpp b/tests/std/include/new_counter.hpp
index 9ecb27607a..a7875a6c23 100644
--- a/tests/std/include/new_counter.hpp
+++ b/tests/std/include/new_counter.hpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
 
 #pragma once
 #pragma warning(push)
diff --git a/tests/std/include/parallel_algorithms_utilities.hpp b/tests/std/include/parallel_algorithms_utilities.hpp
index 1319274c12..f29185d05a 100644
--- a/tests/std/include/parallel_algorithms_utilities.hpp
+++ b/tests/std/include/parallel_algorithms_utilities.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 #include <algorithm>
-#include <stddef.h>
+#include <cstddef>
 #include <thread>
 
 #ifdef EXHAUSTIVE
diff --git a/tests/std/include/test_atomic_wait.hpp b/tests/std/include/test_atomic_wait.hpp
index 740213067e..9322cd5454 100644
--- a/tests/std/include/test_atomic_wait.hpp
+++ b/tests/std/include/test_atomic_wait.hpp
@@ -3,11 +3,11 @@
 
 #pragma once
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
+#include <cstring>
 #include <memory>
-#include <string.h>
 #include <thread>
 
 template <template <class> class Template, class UnderlyingType>
diff --git a/tests/std/include/test_death.hpp b/tests/std/include/test_death.hpp
index 521945a24b..d88f63e9da 100644
--- a/tests/std/include/test_death.hpp
+++ b/tests/std/include/test_death.hpp
@@ -3,9 +3,9 @@
 
 #pragma once
 #include <crtdbg.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/include/test_filesystem_support.hpp b/tests/std/include/test_filesystem_support.hpp
index 7abd557443..3aa5986565 100644
--- a/tests/std/include/test_filesystem_support.hpp
+++ b/tests/std/include/test_filesystem_support.hpp
@@ -6,11 +6,11 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <algorithm>
+#include <cstring>
 #include <experimental/filesystem>
 #include <filesystem>
 #include <iterator>
 #include <random>
-#include <string.h>
 #include <string>
 
 inline std::string get_test_directory_subname(const char* const testName, const size_t testNameLength) {
diff --git a/tests/std/include/test_regex_support.hpp b/tests/std/include/test_regex_support.hpp
index 9367113bcb..fc11c74929 100644
--- a/tests/std/include/test_regex_support.hpp
+++ b/tests/std/include/test_regex_support.hpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #pragma once
+#include <cstdio>
 #include <regex>
-#include <stdio.h>
 #include <string>
 
 class regex_fixture {
diff --git a/tests/std/include/test_thread_support.hpp b/tests/std/include/test_thread_support.hpp
index f92e7ec029..a2e4436346 100644
--- a/tests/std/include/test_thread_support.hpp
+++ b/tests/std/include/test_thread_support.hpp
@@ -5,9 +5,9 @@
 
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
 #include <mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <thread>
 
 #include <Windows.h>
diff --git a/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp b/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
index c4d14581de..4f1f187fd1 100644
--- a/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
+++ b/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 int main() {
diff --git a/tests/std/tests/Dev08_563686_ostream/test.cpp b/tests/std/tests/Dev08_563686_ostream/test.cpp
index 1b5d8b4bd4..48935394f5 100644
--- a/tests/std/tests/Dev08_563686_ostream/test.cpp
+++ b/tests/std/tests/Dev08_563686_ostream/test.cpp
@@ -26,8 +26,8 @@
 
 #define CRTDBG_MAP_ALLOC
 #include <crtdbg.h>
+#include <cstdlib>
 #include <sstream>
-#include <stdlib.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/Dev08_576265_list_remove/test.cpp b/tests/std/tests/Dev08_576265_list_remove/test.cpp
index 6604c0e870..f941f74ebd 100644
--- a/tests/std/tests/Dev08_576265_list_remove/test.cpp
+++ b/tests/std/tests/Dev08_576265_list_remove/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <list>
 
 struct Val {
diff --git a/tests/std/tests/Dev08_584299_search_n/test.cpp b/tests/std/tests/Dev08_584299_search_n/test.cpp
index f072ce2925..332ea5cbc0 100644
--- a/tests/std/tests/Dev08_584299_search_n/test.cpp
+++ b/tests/std/tests/Dev08_584299_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <list>
 
 // This test makes sure that the search_n algorithm behaves correctly.
diff --git a/tests/std/tests/Dev09_012361_vector_swap/test.cpp b/tests/std/tests/Dev09_012361_vector_swap/test.cpp
index 1d1487c215..79f2a0380b 100644
--- a/tests/std/tests/Dev09_012361_vector_swap/test.cpp
+++ b/tests/std/tests/Dev09_012361_vector_swap/test.cpp
@@ -85,14 +85,14 @@
 // deque<int>::iterator: Previously 12, 16, 16, 12, 8. Now 12, 8, 8, 8, 8.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
 #include <deque>
 #include <iterator>
 #include <list>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp b/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
index 784e62e6d1..61137688bd 100644
--- a/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
+++ b/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
@@ -49,9 +49,9 @@
 // correctness to all known cases, and also increases efficiency (as iterator destructors
 // in debug mode with iterator debugging disabled now perform no extra work).
 
-#include <assert.h>
-#include <stdio.h>
-#include <string.h>
+#include <cassert>
+#include <cstdio>
+#include <cstring>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
index b495ef5fd1..ce23d39c16 100644
--- a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
+++ b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <locale>
-#include <stdio.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp b/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
index 51e338de53..b890a5b02a 100644
--- a/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
+++ b/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 
 #include <Windows.h>
diff --git a/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp b/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
index b2a1142577..c36becdb82 100644
--- a/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
+++ b/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 #include <typeinfo>
 
diff --git a/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp b/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
index fdcd0adb81..ea278e06e2 100644
--- a/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
+++ b/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
@@ -1,16 +1,16 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <new>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
diff --git a/tests/std/tests/Dev09_130060_unique_copy/test.cpp b/tests/std/tests/Dev09_130060_unique_copy/test.cpp
index 416e6c5a21..fec2b1f9db 100644
--- a/tests/std/tests/Dev09_130060_unique_copy/test.cpp
+++ b/tests/std/tests/Dev09_130060_unique_copy/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp b/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
index f8e9613c17..433e7edb3c 100644
--- a/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
+++ b/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cmath>
 #include <functional>
-#include <math.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp b/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
index 50abbf1248..4bfb2c260e 100644
--- a/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
+++ b/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
@@ -12,14 +12,14 @@
 // Big is 7 * 64 bits to disable the Small Functor Optimization.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <functional>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp b/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
index 6b726c80d3..16ff6ea8e4 100644
--- a/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
+++ b/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <vector>
 
 struct X {
diff --git a/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp b/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
index 1c45dccac4..90e7d20d9c 100644
--- a/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
+++ b/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <set>
 #include <vector>
 
diff --git a/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp b/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
index 8692ce252c..4c53a27b8d 100644
--- a/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
+++ b/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <climits>
 #include <cmath>
-#include <limits.h>
+#include <cstdlib>
 #include <stdexcept>
-#include <stdlib.h>
 #include <unordered_set>
 #include <utility>
 
diff --git a/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp b/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
index 1c2aa9b953..0ffe77aa7f 100644
--- a/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
+++ b/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <type_traits>
 
diff --git a/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp b/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
index 7baefd4aec..92284ee339 100644
--- a/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
+++ b/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp b/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
index 51f1030009..9e3287e07f 100644
--- a/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
+++ b/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp b/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
index 34d3f6ad7e..d93ec83a81 100644
--- a/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
+++ b/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <utility>
 
diff --git a/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp b/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
index 02bbce8316..068993f7d8 100644
--- a/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp b/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
index 293625f488..c57ae88c8b 100644
--- a/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
+++ b/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <__msvc_all_public_headers.hpp>
-#include <assert.h>
+#include <cassert>
 
 namespace fs = std::experimental::filesystem;
 
diff --git a/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp b/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
index 54abc22c89..203cbb8243 100644
--- a/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
+++ b/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <locale>
 #include <new>
 #include <regex>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp b/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
index 1b4ba4b844..0d63cdb76f 100644
--- a/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
+++ b/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <memory>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp b/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
index 4adb8ad5a7..a37def5946 100644
--- a/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
+++ b/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp b/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
index dd096ed41a..c656f958b2 100644
--- a/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp b/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
index 876abf9d4e..4f6c672be7 100644
--- a/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
+++ b/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp b/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
index 6696e3a4c1..87bbfa53f6 100644
--- a/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
+++ b/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp b/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
index 0859477411..9e59b41b72 100644
--- a/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
+++ b/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <execution>
 #include <random>
-#include <stdint.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp b/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
index f68559a419..b427372a05 100644
--- a/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
+++ b/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp b/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
index edde4cf3d2..3dc91e3c8a 100644
--- a/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
+++ b/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 int main() {
diff --git a/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp b/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
index 00e9cd2785..3e76543f17 100644
--- a/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
+++ b/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <iterator>
 #include <random>
diff --git a/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp b/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
index 374d3dee43..d3f75aaa9d 100644
--- a/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
+++ b/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp b/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
index 14c3fc14ca..2d40860b02 100644
--- a/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
+++ b/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp b/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
index 37dbe23b45..c1b1e2160d 100644
--- a/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <random>
 
diff --git a/tests/std/tests/Dev10_445289_make_shared/test.cpp b/tests/std/tests/Dev10_445289_make_shared/test.cpp
index a9d6722848..ba15fbdd1e 100644
--- a/tests/std/tests/Dev10_445289_make_shared/test.cpp
+++ b/tests/std/tests/Dev10_445289_make_shared/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_482830_header_only_string/test.cpp b/tests/std/tests/Dev10_482830_header_only_string/test.cpp
index ad288fcdd4..33ac64e5a3 100644
--- a/tests/std/tests/Dev10_482830_header_only_string/test.cpp
+++ b/tests/std/tests/Dev10_482830_header_only_string/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cctype>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp b/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
index 89e82bc5a6..8d18750ea3 100644
--- a/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
+++ b/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
@@ -3,9 +3,9 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <functional>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp b/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
index e635248152..5b84891fd9 100644
--- a/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
+++ b/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <new>
-#include <stddef.h>
 #include <tuple>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp b/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
index 38f027d693..eca03193fc 100644
--- a/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
+++ b/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _HAS_AUTO_PTR_ETC 1
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp b/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
index 912c206139..93b4ead540 100644
--- a/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
+++ b/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
@@ -4,12 +4,12 @@
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
 #include <array>
-#include <stddef.h>
-#include <stdlib.h>
+#include <cstddef>
+#include <cstdlib>
 #ifndef _M_CEE_PURE
 #include <atomic>
 #endif // _M_CEE_PURE
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <exception>
 #include <forward_list>
diff --git a/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp b/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
index a2501ca712..e6fd9ac5f9 100644
--- a/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
+++ b/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
@@ -6,7 +6,7 @@
 // family of functions"
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp b/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
index 569adafec8..4dbe0fed13 100644
--- a/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
+++ b/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cmath>
 #include <complex>
+#include <cstdint>
+#include <cstring>
 #include <limits>
-#include <stdint.h>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp b/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
index 8d2f66b285..7eb85025d3 100644
--- a/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
+++ b/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -10,8 +12,6 @@
 #include <memory>
 #include <regex>
 #include <set>
-#include <stddef.h>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/Dev10_562056_tree_leak/test.cpp b/tests/std/tests/Dev10_562056_tree_leak/test.cpp
index d6dcc08c92..1c921104ef 100644
--- a/tests/std/tests/Dev10_562056_tree_leak/test.cpp
+++ b/tests/std/tests/Dev10_562056_tree_leak/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <list>
 #include <map>
diff --git a/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp b/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
index aefed9da8d..9479b7414b 100644
--- a/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
+++ b/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp b/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
index e804e8da02..0fd9c785dc 100644
--- a/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
+++ b/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <set>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp b/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
index d1779c52e5..b6e9b74253 100644
--- a/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
+++ b/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <list>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_590599_hash_string/test.cpp b/tests/std/tests/Dev10_590599_hash_string/test.cpp
index 14b0b5425d..7648542491 100644
--- a/tests/std/tests/Dev10_590599_hash_string/test.cpp
+++ b/tests/std/tests/Dev10_590599_hash_string/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <string>
 
diff --git a/tests/std/tests/Dev10_617014_tuple_tie/test.cpp b/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
index f07d3ff916..d3fd82a55e 100644
--- a/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
+++ b/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev10_632876_regex_proxy/test.cpp b/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
index 2f4f062632..d7ced58681 100644
--- a/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
+++ b/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <new>
 #include <regex>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp b/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
index 0dd30270dc..28f631bb2c 100644
--- a/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
+++ b/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/Dev10_639436_const_map_at/test.cpp b/tests/std/tests/Dev10_639436_const_map_at/test.cpp
index c1a31b9fc9..3ba7d04418 100644
--- a/tests/std/tests/Dev10_639436_const_map_at/test.cpp
+++ b/tests/std/tests/Dev10_639436_const_map_at/test.cpp
@@ -3,10 +3,10 @@
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <hash_map>
 #include <map>
-#include <stdlib.h>
 #include <unordered_map>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp b/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
index 90d2946e39..ca319b0c07 100644
--- a/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
+++ b/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <new>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp b/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
index afcb3029ee..a837847d08 100644
--- a/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
+++ b/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp b/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
index e2a197b78c..654d609b90 100644
--- a/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
+++ b/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp b/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
index e71a41ef43..42b86e6d01 100644
--- a/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
+++ b/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp b/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
index a8653938c6..ec4a1feaa9 100644
--- a/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
+++ b/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <random>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp b/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
index 7bccb57d5b..6703352da5 100644
--- a/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
+++ b/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <list>
 #include <vector>
diff --git a/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp b/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
index b60cebb776..5addf960bd 100644
--- a/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
+++ b/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp b/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
index 23656f129a..a77d72b8c2 100644
--- a/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
+++ b/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
+#include <cstddef>
 #include <deque>
 #include <filesystem>
 #include <forward_list>
@@ -10,7 +11,6 @@
 #include <map>
 #include <set>
 #include <span>
-#include <stddef.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp b/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
index ea7f59a476..6e57a4a996 100644
--- a/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <string>
 
diff --git a/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp b/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
index 8340d994fe..cea9cf2277 100644
--- a/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
+++ b/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
@@ -4,7 +4,7 @@
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <hash_map>
 #include <hash_set>
 #include <map>
diff --git a/tests/std/tests/Dev10_780098_movable_elements/test.cpp b/tests/std/tests/Dev10_780098_movable_elements/test.cpp
index c99688c532..8e03ddc349 100644
--- a/tests/std/tests/Dev10_780098_movable_elements/test.cpp
+++ b/tests/std/tests/Dev10_780098_movable_elements/test.cpp
@@ -1,7 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -9,7 +10,6 @@
 #include <list>
 #include <memory>
 #include <set>
-#include <stddef.h>
 #include <unordered_set>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp b/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
index 639bca1e63..5bbdf31a17 100644
--- a/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
+++ b/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp b/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
index a3ee38ad55..8af8f1deab 100644
--- a/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
+++ b/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
@@ -3,13 +3,13 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <sstream>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp b/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
index 6b3ca253a4..ab6f047f9b 100644
--- a/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
+++ b/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
 #include <regex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 
 #include <test_regex_support.hpp>
diff --git a/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp b/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
index 619ccd9a0f..0bffce7a9d 100644
--- a/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
+++ b/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp b/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
index b64b2b8031..730f44cdaa 100644
--- a/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
+++ b/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp b/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
index 8bee3c01c2..460a4d2e4a 100644
--- a/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
+++ b/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <utility>
 #ifndef _M_CEE_PURE // in /clr:pure we miss runtime coverage of weak_ptr converting constructor
diff --git a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
index b6516c7fad..283dedc4a5 100644
--- a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
+++ b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <bitset>
+#include <cassert>
+#include <cstdlib>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp b/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
index c1857bde5e..3a9e78d92c 100644
--- a/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
+++ b/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp b/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
index d7aa0dbcfd..861bba6b23 100644
--- a/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
+++ b/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp b/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
index 3117a14d06..c3e00928f4 100644
--- a/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
+++ b/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp b/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
index 62b8690bc4..5ce8b908c5 100644
--- a/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
+++ b/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp b/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
index 6bf4cd733e..5a214f0c43 100644
--- a/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
+++ b/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
@@ -3,7 +3,7 @@
 
 // REQUIRES: debug_CRT
 
-#include <assert.h>
+#include <cassert>
 #include <crtdbg.h>
 #include <locale>
 #include <new>
diff --git a/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp b/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
index 9be5001851..a3ba7218d9 100644
--- a/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
+++ b/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp b/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
index 6f02556e5b..72a9a632b3 100644
--- a/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
+++ b/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
@@ -3,13 +3,13 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <list>
-#include <stdlib.h>
 #include <string>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
index 35346dc1b6..f9ea851fcc 100644
--- a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
+++ b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
@@ -5,7 +5,8 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <deque>
 #include <experimental/filesystem>
 #include <filesystem>
@@ -17,7 +18,6 @@
 #include <regex>
 #include <set>
 #include <span>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/Dev11_0000000_quoted/test.cpp b/tests/std/tests/Dev11_0000000_quoted/test.cpp
index b2f0e43c8a..ef08817a42 100644
--- a/tests/std/tests/Dev11_0000000_quoted/test.cpp
+++ b/tests/std/tests/Dev11_0000000_quoted/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <iomanip>
 #include <iostream>
 #include <sstream>
diff --git a/tests/std/tests/Dev11_0000000_rotate_test/test.cpp b/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
index 253c1d2ad3..91f203095f 100644
--- a/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
+++ b/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
@@ -17,7 +17,7 @@
 // -5- Complexity: At most last - first swaps.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp b/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
index 6ed6101118..4258b875f6 100644
--- a/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
+++ b/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <string>
diff --git a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
index e6e6b0d214..aea1fb6530 100644
--- a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
+++ b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
@@ -8,7 +8,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <complex>
 #include <cstddef>
diff --git a/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp b/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
index ab6d5f6ef0..674940b1ed 100644
--- a/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
+++ b/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
@@ -14,7 +14,7 @@
 // a value-initialized iterator as the source of a copy or move operation."
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <forward_list>
 #include <list>
diff --git a/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp b/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
index c6035cd7e1..39e3a7f560 100644
--- a/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
+++ b/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <stdexcept>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp b/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
index e4a542d630..e5af4b6949 100644
--- a/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
+++ b/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp b/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
index 43dfd67165..4492721074 100644
--- a/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
+++ b/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <random>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp b/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
index 80a77115a3..0fdd2df70d 100644
--- a/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
+++ b/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdlib>
 #include <functional>
 #include <future>
 #include <memory>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
 #include <thread>
diff --git a/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp b/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
index 6e66216ced..63aa3516a4 100644
--- a/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
+++ b/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
@@ -4,7 +4,7 @@
 // DevDiv-253803 "<algorithm>: merge() asserts when given null src/dest"
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp b/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
index fa050292eb..dd67957c7b 100644
--- a/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
+++ b/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp b/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
index e5d7ba58b1..664fe80360 100644
--- a/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
+++ b/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <new>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0302476_pair_move/test.cpp b/tests/std/tests/Dev11_0302476_pair_move/test.cpp
index a0d34d4559..479294924d 100644
--- a/tests/std/tests/Dev11_0302476_pair_move/test.cpp
+++ b/tests/std/tests/Dev11_0302476_pair_move/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <tuple>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp b/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
index f46def52bc..a3adc62e70 100644
--- a/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
+++ b/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <tuple>
diff --git a/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp b/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
index 88bb3637ad..266509eb65 100644
--- a/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
+++ b/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
@@ -15,7 +15,7 @@
 #endif // __clang__
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <climits>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp b/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
index 6ed18c2416..2fbf27bb44 100644
--- a/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
+++ b/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
@@ -8,7 +8,7 @@
 // [...]
 // - otherwise, the value is tid and its type Vi is TiD cv &.
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 
diff --git a/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp b/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
index d1c0d64c9f..23b90ea421 100644
--- a/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
+++ b/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <future>
 #include <memory>
diff --git a/tests/std/tests/Dev11_0387701_container_equality/test.cpp b/tests/std/tests/Dev11_0387701_container_equality/test.cpp
index 6d00e3d2b5..ee733eb0e0 100644
--- a/tests/std/tests/Dev11_0387701_container_equality/test.cpp
+++ b/tests/std/tests/Dev11_0387701_container_equality/test.cpp
@@ -5,7 +5,8 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -15,7 +16,6 @@
 #include <map>
 #include <random>
 #include <set>
-#include <stddef.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0437519_container_behavior/test.cpp b/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
index 1d6751311d..8a6e1f238d 100644
--- a/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
+++ b/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp b/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
index fe73ee5ddd..b9b08f29ec 100644
--- a/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
+++ b/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <codecvt>
 #include <locale>
 #include <new>
diff --git a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
index a323504ec1..a643e89601 100644
--- a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
+++ b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <set>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp b/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
index 465c1b4c16..07b770d598 100644
--- a/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
+++ b/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
 #include <crtdbg.h>
+#include <cstdlib>
 #include <functional>
 #include <list>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp b/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
index 8800997059..59aa7eea9b 100644
--- a/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
+++ b/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
-#include <ctype.h>
+#include <cassert>
+#include <cctype>
 #include <ios>
 #include <system_error>
 
diff --git a/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp b/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
index ca4304f61b..9e147d89e3 100644
--- a/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
+++ b/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <ctime>
 #include <iterator>
 #include <locale>
 #include <sstream>
 #include <string>
-#include <time.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
index f4c61f86cb..c7ac08d39e 100644
--- a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
+++ b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <clocale>
+#include <cstdio>
 #include <exception>
-#include <locale.h>
 #include <locale>
 #include <sstream>
-#include <stdio.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0532622_minmax_element/test.cpp b/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
index eacba1e0e2..1a2964283d 100644
--- a/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
+++ b/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
@@ -16,7 +16,7 @@
 // where M is the last iterator in [first,last) such that no iterator in the range refers to a larger element."
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp b/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
index fee7a245a5..055718cc9a 100644
--- a/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
+++ b/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
@@ -6,10 +6,10 @@
 #define _SILENCE_CXX17_ADAPTOR_TYPEDEFS_DEPRECATION_WARNING
 #define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <memory>
-#include <stdlib.h>
 #include <string>
 #include <type_traits>
 #include <typeinfo>
diff --git a/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp b/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
index f2c04f61e7..9e4be783a6 100644
--- a/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
+++ b/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
@@ -7,9 +7,9 @@
 // restricted to the coarser of the precisions of time_t and time_point. It is
 // implementation defined whether values are rounded or truncated to the required precision."
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
-#include <stdint.h>
+#include <cstdint>
 
 using namespace std;
 using namespace std::chrono;
diff --git a/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp b/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
index 8cd793c417..6cff3d0e2d 100644
--- a/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
+++ b/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <random>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp b/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
index 6906568996..253d9ad60c 100644
--- a/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
+++ b/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
@@ -3,10 +3,10 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
 #include <new>
-#include <stdint.h>
-#include <stdlib.h>
 
 #if _HAS_CXX17 && !defined(_M_CEE)
 #define HAS_PARALLEL_ALGORITHMS 1
diff --git a/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp b/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
index 76ee02195e..1189dd0359 100644
--- a/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
+++ b/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
@@ -22,7 +22,7 @@
 // tuple(const tuple&) = default;
 // tuple(tuple&&) = default;
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp b/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
index e0e0c218f8..16ae8abdb4 100644
--- a/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
+++ b/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp b/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
index 3180079730..0cf5fb7d51 100644
--- a/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
+++ b/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev11_0671816_list_splice/test.cpp b/tests/std/tests/Dev11_0671816_list_splice/test.cpp
index 29679a5918..a6f5cc8b58 100644
--- a/tests/std/tests/Dev11_0671816_list_splice/test.cpp
+++ b/tests/std/tests/Dev11_0671816_list_splice/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp b/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
index d8a4987cb9..59445210f1 100644
--- a/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
+++ b/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <future>
 
diff --git a/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp b/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
index ca7ba6f3c8..7572be3adf 100644
--- a/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
+++ b/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <map>
 #include <new>
 #include <set>
-#include <stddef.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
index 844be31d86..38263938ca 100644
--- a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
+++ b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
@@ -5,13 +5,13 @@
 
 #define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <crtdbg.h>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <functional>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp b/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
index 5d4eaf1a28..07c66ed99b 100644
--- a/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
+++ b/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <map>
 #include <set>
-#include <stddef.h>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev11_0835323_to_string/test.cpp b/tests/std/tests/Dev11_0835323_to_string/test.cpp
index e57504dc87..10d52236e7 100644
--- a/tests/std/tests/Dev11_0835323_to_string/test.cpp
+++ b/tests/std/tests/Dev11_0835323_to_string/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cmath>
+#include <cstdlib>
 #include <limits>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0836436_get_time/test.cpp b/tests/std/tests/Dev11_0836436_get_time/test.cpp
index 0e332887e6..cdd71673f1 100644
--- a/tests/std/tests/Dev11_0836436_get_time/test.cpp
+++ b/tests/std/tests/Dev11_0836436_get_time/test.cpp
@@ -1,16 +1,16 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdio>
 #include <cstdlib>
+#include <ctime>
 #include <iomanip>
 #include <ios>
 #include <locale>
 #include <sstream>
 #include <streambuf>
 #include <string>
-#include <time.h>
 #include <tuple>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp b/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
index ee421c1135..57c08b074c 100644
--- a/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
+++ b/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
@@ -7,14 +7,14 @@
 // improvements. This test verifies scanf-printf round-tripping of a set of
 // diverse floating point values (both single and double precision).
 
-#include <assert.h>
-#include <float.h>
+#include <cassert>
+#include <cfloat>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
 #include <iomanip>
 #include <ios>
-#include <math.h>
 #include <sstream>
-#include <stdint.h>
-#include <stdio.h>
 
 #include <floating_point_test_cases.hpp>
 
diff --git a/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp b/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
index 0516b39f3e..aaa0ae769e 100644
--- a/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
+++ b/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
@@ -6,13 +6,13 @@
 // Regress\intrin\atomic.cpp
 //
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
 #include <limits>
 #include <new>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 
 
diff --git a/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp b/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
index d1c74c1e5a..1be18dcf82 100644
--- a/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
+++ b/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
@@ -7,7 +7,9 @@
 #define _SILENCE_CXX17_OLD_ALLOCATOR_MEMBERS_DEPRECATION_WARNING
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -19,8 +21,6 @@
 #include <random>
 #include <regex>
 #include <set>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/Dev11_1003120_search_test/test.cpp b/tests/std/tests/Dev11_1003120_search_test/test.cpp
index b0f904a2ae..b65aa27e4f 100644
--- a/tests/std/tests/Dev11_1003120_search_test/test.cpp
+++ b/tests/std/tests/Dev11_1003120_search_test/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stdlib.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp b/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
index a74471c05a..097f9dd14c 100644
--- a/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
+++ b/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
@@ -3,8 +3,8 @@
 
 #define _SILENCE_CXX20_OLD_SHARED_PTR_ATOMIC_SUPPORT_DEPRECATION_WARNING
 
+#include <cstdlib>
 #include <memory>
-#include <stdlib.h>
 
 #ifndef _M_CEE_PURE
 #include <atomic>
diff --git a/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp b/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
index e4f6a4f33d..27300609c4 100644
--- a/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
+++ b/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
@@ -3,13 +3,13 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdint>
+#include <cstdio>
 #include <experimental/filesystem>
 #include <filesystem>
 #include <fstream>
-#include <stdint.h>
-#include <stdio.h>
 #include <string>
 #include <system_error>
 
diff --git a/tests/std/tests/Dev11_1074023_constexpr/test.cpp b/tests/std/tests/Dev11_1074023_constexpr/test.cpp
index 5bd52e78b6..1386ab3c22 100644
--- a/tests/std/tests/Dev11_1074023_constexpr/test.cpp
+++ b/tests/std/tests/Dev11_1074023_constexpr/test.cpp
@@ -9,7 +9,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #ifndef _M_CEE_PURE
 #include <atomic>
 #endif // _M_CEE_PURE
@@ -29,12 +29,12 @@
 #ifndef _M_CEE
 #include <mutex>
 #endif // _M_CEE
+#include <cstdint>
 #include <new>
 #include <numeric>
 #include <random>
 #include <ratio>
 #include <regex>
-#include <stdint.h>
 #include <string>
 #include <system_error>
 #include <tuple>
diff --git a/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp b/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
index 35c969fc23..071ad45f30 100644
--- a/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
+++ b/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <chrono>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <functional>
 #include <intrin0.h>
 #include <mutex>
 #include <stdexcept>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <thread>
 #include <vector>
diff --git a/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp b/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
index 8b86d403d0..757c4bbec3 100644
--- a/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
+++ b/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
@@ -3,11 +3,11 @@
 
 // Test DevDiv-1114006 "[+ VS2015] conditional_variable with predicate does not behave according to the standard".
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdlib>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp b/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
index ee3eb561b9..dbcb0d8f41 100644
--- a/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
+++ b/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
@@ -6,7 +6,7 @@
 // This test validates the implementation of std::uncaught_exceptions by recursively
 // throwing exceptions from a destructor.
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 
 class awesome_exception {};
diff --git a/tests/std/tests/Dev11_1137366_nested_exception/test.cpp b/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
index fe8a39c6e8..ebc04730f7 100644
--- a/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
+++ b/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <type_traits>
 #include <typeinfo>
diff --git a/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp b/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
index 520b18debb..eebeebf7a6 100644
--- a/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
+++ b/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp b/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
index 721a217a1f..55d463d44d 100644
--- a/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
+++ b/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
 #include <mutex>
 #include <shared_mutex>
diff --git a/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp b/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
index b0c51f8e08..6da04e5bb1 100644
--- a/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
+++ b/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <regex>
 #include <thread>
 #include <vector>
diff --git a/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp b/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
index ae25b35801..d6c7d2d200 100644
--- a/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
+++ b/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <experimental/filesystem>
 #include <fstream>
diff --git a/tests/std/tests/GH_000457_system_error_message/test.cpp b/tests/std/tests/GH_000457_system_error_message/test.cpp
index 234115aa39..76c65980b8 100644
--- a/tests/std/tests/GH_000457_system_error_message/test.cpp
+++ b/tests/std/tests/GH_000457_system_error_message/test.cpp
@@ -4,7 +4,7 @@
 #include <yvals.h>
 
 #include <__msvc_system_error_abi.hpp>
-#include <assert.h>
+#include <cassert>
 
 int main() {
     char example[] = "test string \r\n\t\0 test test";
diff --git a/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp b/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
index 4b6f623d19..7e9d8f395a 100644
--- a/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
+++ b/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstdlib>
 #include <vector>
 
diff --git a/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp b/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
index c1f995cc1c..b2c0b66cf0 100644
--- a/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
+++ b/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
@@ -5,8 +5,8 @@
 
 #include <cassert>
 #include <cfenv>
+#include <cfloat>
 #include <cmath>
-#include <float.h>
 #include <type_traits>
 #include <xutility>
 
diff --git a/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp b/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
index a823c2599a..656b95c5d6 100644
--- a/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
+++ b/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 #include <filesystem>
 #include <string_view>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
index ef17b13b40..ac14629d80 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <numeric>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
index fdf114291e..2cdf0d5441 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
index fbf511c823..0206f7025d 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
index 3d277ccf3f..6252f6e463 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <list>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
index 9e1cadc49e..45fd84742e 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
index 10d84d3372..cdb0c7578d 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
index 97aa3f3e07..6f6de1ed09 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
index b3f4597ebb..1e269d1bf3 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
index 3983d04532..e4516709d2 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <list>
 #include <numeric>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
index b4f3d6910d..ecfbea2801 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
index 4745a28693..eddb7b3b6b 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
index ed8fd50cdf..25f8464e98 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <numeric>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
index 8b0181988d..c3d08f94e6 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
index cf13143613..b733540f21 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
@@ -2,7 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <execution>
 #include <forward_list>
@@ -10,7 +11,6 @@
 #include <iterator>
 #include <list>
 #include <numeric>
-#include <stddef.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
index 40340d755d..cac22c3ab7 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
index 345f2c2171..1a3b53c758 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
index 3d8cc29fe7..c168a294f2 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
@@ -3,7 +3,7 @@
 
 #pragma warning(disable : 4242 4244 4365) // test_case_incorrect_special_case_reasoning tests narrowing on purpose
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
index a0d735e6c6..953bbd5a17 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
index d65b48cae8..1a4c38389a 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <random>
 #include <vector>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
index ab5e44b0b9..df56ffa6a3 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
index 46809e70ef..dd7ed5433a 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
index c641e892d4..27cd4f78b2 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <functional>
 #include <iostream>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
index 373c3997a1..713b6978ab 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <functional>
 #include <iostream>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
index b3d614b1a2..c74a8c7fd5 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <numeric>
 #include <random>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
index 0bf345291f..2ffb607160 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <list>
 #include <random>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
index 88a1775fe5..b901786db8 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
index 77c64ceb2e..c124c9ad4b 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
index 0cd78e77a6..d4e299dc5a 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
index 393e077b57..9141838019 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
@@ -3,7 +3,7 @@
 
 #pragma warning(disable : 4242 4244 4365) // test_case_incorrect_special_case_reasoning tests narrowing on purpose
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
index 7a21362fb2..ac66ca4024 100644
--- a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
+++ b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
@@ -7,7 +7,7 @@
 #define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp b/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
index d555097157..8fcd62f428 100644
--- a/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
+++ b/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <memory>
 #include <new>
diff --git a/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp b/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
index beffa7170d..6ba46a2457 100644
--- a/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
+++ b/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <ios>
diff --git a/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp b/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
index 7be213814d..40c4778f6e 100644
--- a/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
+++ b/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
@@ -5,7 +5,7 @@
 #define DOUBLE_FROM_CHARS_TEST_CASES_HPP
 
 #include <charconv>
-#include <stddef.h>
+#include <cstddef>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp b/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
index 0acbef1688..5bd6f23f88 100644
--- a/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
+++ b/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
@@ -5,7 +5,7 @@
 #define FLOAT_FROM_CHARS_TEST_CASES_HPP
 
 #include <charconv>
-#include <stddef.h>
+#include <cstddef>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0067R5_charconv/test.cpp b/tests/std/tests/P0067R5_charconv/test.cpp
index d58194240f..400c1f62a5 100644
--- a/tests/std/tests/P0067R5_charconv/test.cpp
+++ b/tests/std/tests/P0067R5_charconv/test.cpp
@@ -5,10 +5,14 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <charconv>
 #include <chrono>
 #include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <fstream>
 #include <functional>
 #include <limits>
@@ -16,10 +20,6 @@
 #include <optional>
 #include <random>
 #include <set>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0067R5_charconv/test.hpp b/tests/std/tests/P0067R5_charconv/test.hpp
index 398533acfc..8662971aa0 100644
--- a/tests/std/tests/P0067R5_charconv/test.hpp
+++ b/tests/std/tests/P0067R5_charconv/test.hpp
@@ -5,8 +5,8 @@
 #define TEST_HPP
 
 #include <charconv>
+#include <cstddef>
 #include <limits>
-#include <stddef.h>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp b/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
index 64a8c05e22..77054bb4ae 100644
--- a/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
+++ b/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
 #include <functional>
 #include <initializer_list>
 #include <iterator>
 #include <map>
 #include <memory>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
 #include <type_traits>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/P0092R1_polishing_chrono/test.cpp b/tests/std/tests/P0092R1_polishing_chrono/test.cpp
index 90fef1c564..f43668efa8 100644
--- a/tests/std/tests/P0092R1_polishing_chrono/test.cpp
+++ b/tests/std/tests/P0092R1_polishing_chrono/test.cpp
@@ -5,10 +5,10 @@
 // Tests the new functions added as part of P0092R1, "Polishing Chrono"
 //
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdint>
 #include <ratio>
-#include <stdint.h>
 
 using namespace std;
 using namespace std::chrono;
diff --git a/tests/std/tests/P0122R7_span_death/test.cpp b/tests/std/tests/P0122R7_span_death/test.cpp
index 619dae9b52..545b6729de 100644
--- a/tests/std/tests/P0122R7_span_death/test.cpp
+++ b/tests/std/tests/P0122R7_span_death/test.cpp
@@ -4,8 +4,8 @@
 #define _CONTAINER_DEBUG_LEVEL 1
 
 #include <algorithm>
+#include <cstddef>
 #include <span>
-#include <stddef.h>
 #include <vector>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/P0137R1_launder/test.cpp b/tests/std/tests/P0137R1_launder/test.cpp
index 0eb5ef4336..8165c51d03 100644
--- a/tests/std/tests/P0137R1_launder/test.cpp
+++ b/tests/std/tests/P0137R1_launder/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <new>
 
 using namespace std;
diff --git a/tests/std/tests/P0156R2_scoped_lock/test.cpp b/tests/std/tests/P0156R2_scoped_lock/test.cpp
index 2483e2e7a6..1248533591 100644
--- a/tests/std/tests/P0156R2_scoped_lock/test.cpp
+++ b/tests/std/tests/P0156R2_scoped_lock/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <atomic>
+#include <cstdlib>
 #include <iostream>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp b/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
index d7615f245a..dc51b5ce3f 100644
--- a/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
+++ b/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/P0218R1_filesystem/test.cpp b/tests/std/tests/P0218R1_filesystem/test.cpp
index 028a08ca5d..1208bfb0ae 100644
--- a/tests/std/tests/P0218R1_filesystem/test.cpp
+++ b/tests/std/tests/P0218R1_filesystem/test.cpp
@@ -4,8 +4,10 @@
 #define _SILENCE_CXX20_U8PATH_DEPRECATION_WARNING
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdlib>
+#include <cstring>
 #include <cvt/cp1251>
 #include <cvt/sjis>
 #include <cvt/utf8_utf16>
@@ -18,8 +20,6 @@
 #include <memory>
 #include <optional>
 #include <sstream>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0220R1_sample/test.cpp b/tests/std/tests/P0220R1_sample/test.cpp
index ffe03d2635..007b9d5280 100644
--- a/tests/std/tests/P0220R1_sample/test.cpp
+++ b/tests/std/tests/P0220R1_sample/test.cpp
@@ -3,11 +3,11 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <iterator>
 #include <numeric>
 #include <random>
-#include <stdio.h>
 #include <type_traits>
 
 #include "adapterator.hpp"
diff --git a/tests/std/tests/P0220R1_searchers/test.cpp b/tests/std/tests/P0220R1_searchers/test.cpp
index f6bf62056e..b2ae5aa387 100644
--- a/tests/std/tests/P0220R1_searchers/test.cpp
+++ b/tests/std/tests/P0220R1_searchers/test.cpp
@@ -2,16 +2,16 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstddef>
+#include <cstdint>
 #include <forward_list>
 #include <functional>
 #include <initializer_list>
 #include <iostream>
 #include <iterator>
 #include <random>
-#include <stddef.h>
-#include <stdint.h>
 #include <string>
 #include <string_view>
 #include <utility>
diff --git a/tests/std/tests/P0220R1_string_view/test.cpp b/tests/std/tests/P0220R1_string_view/test.cpp
index 3a490ed738..f7ffb3ee21 100644
--- a/tests/std/tests/P0220R1_string_view/test.cpp
+++ b/tests/std/tests/P0220R1_string_view/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <sstream>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp b/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
index 51c990f976..27949e667b 100644
--- a/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
+++ b/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <limits.h>
+#include <climits>
 #include <numeric>
 
 using std::gcd;
diff --git a/tests/std/tests/P0325R4_to_array/test.cpp b/tests/std/tests/P0325R4_to_array/test.cpp
index 78c70b53e9..ccdbbdcecb 100644
--- a/tests/std/tests/P0325R4_to_array/test.cpp
+++ b/tests/std/tests/P0325R4_to_array/test.cpp
@@ -3,7 +3,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <type_traits>
diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
index 42e52cbf32..b97c7c8231 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <clocale>
 #include <concepts>
+#include <cstdio>
 #include <format>
 #include <iostream>
 #include <locale>
 #include <sstream>
-#include <stdio.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/P0356R5_bind_front/test.cpp b/tests/std/tests/P0356R5_bind_front/test.cpp
index 804c9c3bb6..c6ad4e785d 100644
--- a/tests/std/tests/P0356R5_bind_front/test.cpp
+++ b/tests/std/tests/P0356R5_bind_front/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <string>
diff --git a/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp b/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
index d04ff491b5..e3c2f6570e 100644
--- a/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
+++ b/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <memory>
 #include <sstream>
diff --git a/tests/std/tests/P0415R1_constexpr_complex/test.cpp b/tests/std/tests/P0415R1_constexpr_complex/test.cpp
index e02267a93f..12383dfc80 100644
--- a/tests/std/tests/P0415R1_constexpr_complex/test.cpp
+++ b/tests/std/tests/P0415R1_constexpr_complex/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <complex>
 #include <type_traits>
 using namespace std;
diff --git a/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp b/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
index 4a03e8e6b7..c3153c7e86 100644
--- a/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
+++ b/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/P0433R2_deduction_guides/test.cpp b/tests/std/tests/P0433R2_deduction_guides/test.cpp
index 37cd60f656..db6aabc226 100644
--- a/tests/std/tests/P0433R2_deduction_guides/test.cpp
+++ b/tests/std/tests/P0433R2_deduction_guides/test.cpp
@@ -2,10 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <chrono>
 #include <complex>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -21,7 +22,6 @@
 #include <set>
 #include <sstream>
 #include <stack>
-#include <stddef.h>
 #include <streambuf>
 #include <string>
 #include <string_view>
diff --git a/tests/std/tests/P0448R4_spanstream/test.cpp b/tests/std/tests/P0448R4_spanstream/test.cpp
index 4355df2f6d..1dba07b485 100644
--- a/tests/std/tests/P0448R4_spanstream/test.cpp
+++ b/tests/std/tests/P0448R4_spanstream/test.cpp
@@ -3,7 +3,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <ios>
 #include <limits>
 #include <span>
diff --git a/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp b/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
index f5cef24bce..f1ee5890b8 100644
--- a/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
+++ b/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
@@ -1,6 +1,6 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/P0476R2_bit_cast/test.cpp b/tests/std/tests/P0476R2_bit_cast/test.cpp
index 4135f0f2ed..612846b41f 100644
--- a/tests/std/tests/P0476R2_bit_cast/test.cpp
+++ b/tests/std/tests/P0476R2_bit_cast/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <cmath>
+#include <cstddef>
+#include <cstring>
 #include <limits>
-#include <stddef.h>
-#include <string.h>
 #include <type_traits>
 #include <utility>
 
diff --git a/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp b/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
index edd2970860..00f8f4ae32 100644
--- a/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
+++ b/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <istream>
 #include <iterator>
 #include <sstream>
diff --git a/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp b/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
index 40edfba826..a94452d8f6 100644
--- a/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
+++ b/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
@@ -4,12 +4,12 @@
 #define _HAS_DEPRECATED_ADAPTOR_TYPEDEFS 1
 #define _SILENCE_CXX17_ADAPTOR_TYPEDEFS_DEPRECATION_WARNING
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <memory>
 #include <optional>
-#include <stddef.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp b/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
index c73cccfa76..2d924ccc9f 100644
--- a/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
+++ b/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <limits>
 
 using namespace std;
diff --git a/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp b/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
index 40bbfc0f00..983145ab42 100644
--- a/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
+++ b/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <limits>
 #include <utility>
 
diff --git a/tests/std/tests/P0586R2_integer_comparison/test.cpp b/tests/std/tests/P0586R2_integer_comparison/test.cpp
index 247172472a..5522fe00a7 100644
--- a/tests/std/tests/P0586R2_integer_comparison/test.cpp
+++ b/tests/std/tests/P0586R2_integer_comparison/test.cpp
@@ -5,9 +5,9 @@
 // Tests the new functions added as part of P0586R2, "Integer Comparison Functions"
 //
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <limits>
-#include <stdint.h>
 #include <utility>
 using namespace std;
 
diff --git a/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp b/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
index 1af2be0478..8f44b81f0b 100644
--- a/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
+++ b/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 using namespace std;
 
diff --git a/tests/std/tests/P0607R0_inline_variables/test.cpp b/tests/std/tests/P0607R0_inline_variables/test.cpp
index cb28fc0b70..899d73728e 100644
--- a/tests/std/tests/P0607R0_inline_variables/test.cpp
+++ b/tests/std/tests/P0607R0_inline_variables/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp b/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
index 59600dd93c..b5f1f734c7 100644
--- a/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
+++ b/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
@@ -3,8 +3,8 @@
 
 // Also tests for P1957R2: Converting from T* to bool should be considered narrowing
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <functional>
 #include <optional>
 #include <string>
diff --git a/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp b/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
index 58100b4314..c89b53526f 100644
--- a/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
+++ b/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <numeric>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/P0645R10_text_formatting_args/test.cpp b/tests/std/tests/P0645R10_text_formatting_args/test.cpp
index d5ba4e427f..85a1784d7b 100644
--- a/tests/std/tests/P0645R10_text_formatting_args/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_args/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <cstdint>
diff --git a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
index 78bcc07288..39f946fa14 100644
--- a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <format>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/P0645R10_text_formatting_death/test.cpp b/tests/std/tests/P0645R10_text_formatting_death/test.cpp
index e597f994cd..e72fab0920 100644
--- a/tests/std/tests/P0645R10_text_formatting_death/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_death/test.cpp
@@ -3,7 +3,7 @@
 
 #define _CONTAINER_DEBUG_LEVEL 1
 
-#include <assert.h>
+#include <cassert>
 #include <format>
 #include <string_view>
 
diff --git a/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp b/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
index c68b91a0c1..224282a9e7 100644
--- a/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <format>
 #include <iterator>
 #include <span>
-#include <stddef.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp b/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
index c587832f85..d0ec2134ce 100644
--- a/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <format>
diff --git a/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp b/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
index 5606ea8592..58bbf2049f 100644
--- a/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
+++ b/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
 #include <mutex>
-#include <stdio.h>
 #include <thread>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/P0660R10_stop_token/test.cpp b/tests/std/tests/P0660R10_stop_token/test.cpp
index d19e29fa9d..132dd856a2 100644
--- a/tests/std/tests/P0660R10_stop_token/test.cpp
+++ b/tests/std/tests/P0660R10_stop_token/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
+#include <cstdio>
 #include <optional>
-#include <stdio.h>
 #include <stop_token>
 #include <thread>
 #include <utility>
diff --git a/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp b/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
index 8c8811d7c9..35f23ecc50 100644
--- a/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
+++ b/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdint>
 #include <memory>
 #include <thread>
diff --git a/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp b/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
index bdcd7dae5c..f77bc7a19b 100644
--- a/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
+++ b/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <ios>
 #include <memory>
 #include <sstream>
diff --git a/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp b/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
index deaa8f3be4..96b62982c8 100644
--- a/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
+++ b/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/P0784R7_library_machinery/test.cpp b/tests/std/tests/P0784R7_library_machinery/test.cpp
index da35eedb8c..86e8d22922 100644
--- a/tests/std/tests/P0784R7_library_machinery/test.cpp
+++ b/tests/std/tests/P0784R7_library_machinery/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp b/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
index 7fae144a0c..a91077e6c8 100644
--- a/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
+++ b/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
 #include <limits>
 #include <memory>
 #include <span>
-#include <stddef.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/P0811R3_midpoint_lerp/test.cpp b/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
index df985c286c..e519fc6964 100644
--- a/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
+++ b/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
@@ -2,18 +2,18 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <bit>
+#include <cassert>
+#include <cfenv>
 #include <charconv>
 #include <cmath>
-#include <fenv.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <iterator>
 #include <limits>
 #include <numeric>
 #include <optional>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp b/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
index 2428941aee..9869f0f6b1 100644
--- a/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <compare>
 #include <concepts>
 #include <iterator>
diff --git a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
index 5955b6ce99..1f4582483c 100644
--- a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <compare>
 #include <concepts>
 #include <cstddef>
diff --git a/tests/std/tests/P0896R4_ranges_to_address/test.cpp b/tests/std/tests/P0896R4_ranges_to_address/test.cpp
index 34070d3688..c9bda4a252 100644
--- a/tests/std/tests/P0896R4_ranges_to_address/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_to_address/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <type_traits>
diff --git a/tests/std/tests/P0898R3_concepts/test.cpp b/tests/std/tests/P0898R3_concepts/test.cpp
index f6b8c591ad..1a15e0830e 100644
--- a/tests/std/tests/P0898R3_concepts/test.cpp
+++ b/tests/std/tests/P0898R3_concepts/test.cpp
@@ -9,8 +9,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <cstdio>
diff --git a/tests/std/tests/P0898R3_identity/test.cpp b/tests/std/tests/P0898R3_identity/test.cpp
index cb45383895..648858c291 100644
--- a/tests/std/tests/P0898R3_identity/test.cpp
+++ b/tests/std/tests/P0898R3_identity/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/P0912R5_coroutine/test.cpp b/tests/std/tests/P0912R5_coroutine/test.cpp
index d448c8f2b4..0a0933cd84 100644
--- a/tests/std/tests/P0912R5_coroutine/test.cpp
+++ b/tests/std/tests/P0912R5_coroutine/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <coroutine>
 #include <exception>
 using namespace std;
diff --git a/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp b/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
index a41a511799..681d6e290d 100644
--- a/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
+++ b/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <hash_map>
 #include <hash_set>
diff --git a/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp b/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
index 7f5d00ebda..4b77954ce9 100644
--- a/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
+++ b/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_CXX20_STRING_RESERVE_WITHOUT_ARGUMENT_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/P1004R2_constexpr_vector/test.cpp b/tests/std/tests/P1004R2_constexpr_vector/test.cpp
index 4549f9068c..12a8d2ea66 100644
--- a/tests/std/tests/P1004R2_constexpr_vector/test.cpp
+++ b/tests/std/tests/P1004R2_constexpr_vector/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp b/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
index 4a155ad2cb..17c3d03e80 100644
--- a/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
+++ b/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/P1007R3_assume_aligned/test.cpp b/tests/std/tests/P1007R3_assume_aligned/test.cpp
index a878589d1f..aa8cae4d23 100644
--- a/tests/std/tests/P1007R3_assume_aligned/test.cpp
+++ b/tests/std/tests/P1007R3_assume_aligned/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <memory>
-#include <stddef.h>
 
 constexpr void can_change_value_via_assume_aligned(int* p) {
     int* p1 = std::assume_aligned<256>(p);
diff --git a/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp b/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
index c6ee3f4c3c..39371d080e 100644
--- a/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
+++ b/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
diff --git a/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp b/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
index b66ebf80fc..f2ff62aa6e 100644
--- a/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
+++ b/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <memory>
-#include <stddef.h>
 #include <string_view>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp b/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
index 746969b872..f583785499 100644
--- a/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
+++ b/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <memory>
-#include <stddef.h>
 #include <stdexcept>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
index dbedbec1df..c768004463 100644
--- a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
+++ b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
@@ -92,8 +92,8 @@ import <vector>;
 import <version>;
 // clang-format on
 
-#include <assert.h>
-#include <stdio.h>
+#include <assert.h> // intentionally not <cassert>
+#include <stdio.h> // intentionally not <cstdio>
 
 #include <force_include.hpp>
 using namespace std;
diff --git a/tests/std/tests/P1645R1_constexpr_numeric/test.cpp b/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
index 20ffd6fbab..8a5842a193 100644
--- a/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
+++ b/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <iterator>
 #include <numeric>
-#include <stddef.h>
 #include <utility>
 
 using namespace std;
diff --git a/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp b/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
index 79b16fa691..77ab2d93b0 100644
--- a/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
+++ b/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <optional>
 #include <type_traits>
diff --git a/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp b/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
index 627143040e..b220fc08da 100644
--- a/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
+++ b/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
@@ -2,7 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -12,8 +14,6 @@
 #include <map>
 #include <new>
 #include <set>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp b/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
index 942a4d4d0e..89fcc3e520 100644
--- a/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
+++ b/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <any>
-#include <assert.h>
+#include <cassert>
 #include <utility>
 
 #include "ab.hpp"
diff --git a/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp b/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
index 22a4e69a80..8555e30670 100644
--- a/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
+++ b/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
@@ -1,14 +1,14 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <thread>
 #include <utility>
 
diff --git a/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp b/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
index 8a00c071f4..12d0d3811a 100644
--- a/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
+++ b/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -11,8 +13,6 @@
 #include <map>
 #include <new>
 #include <set>
-#include <stdio.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp b/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
index 03399bb667..6052ab4a49 100644
--- a/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
+++ b/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <excpt.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp b/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
index 00f5423fcf..f3c0d19a44 100644
--- a/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
+++ b/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 #include <functional>
 #include <memory>
diff --git a/tests/std/tests/VSO_0000000_initialize_everything/test.cpp b/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
index 4341869d22..dea3354881 100644
--- a/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
+++ b/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
 #include <initializer_list>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <string.h>
 #include <string>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp b/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
index ab1c282261..8c800b3c6b 100644
--- a/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
+++ b/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <stdexcept>
-#include <stdlib.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp b/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
index c86c4fc27d..33bb2deb78 100644
--- a/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
+++ b/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <forward_list>
 #include <initializer_list>
 #include <list>
 #include <set>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
index c0588a85e3..b6a7c77915 100644
--- a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
+++ b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
-#include <stddef.h>
+#include <cassert>
+#include <cstddef>
 #include <string>
 
 extern "C" {
diff --git a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
index be6171dbc3..9dab1d60db 100644
--- a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
+++ b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #ifndef _M_CEE
 #include <mutex>
diff --git a/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp b/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
index 3646a6e51b..52e074acd4 100644
--- a/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
+++ b/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <iosfwd>
 #include <istream>
 #include <ostream>
diff --git a/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp b/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
index 495b9de28a..9b11b5c280 100644
--- a/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
+++ b/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_FPOS_SEEKPOS_DEPRECATION_WARNING
-#include <assert.h>
+#include <cassert>
 #include <iosfwd>
 
 int main() {
diff --git a/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp b/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
index 024d6152f2..53b9f6576f 100644
--- a/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
+++ b/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <experimental/filesystem>
 #include <fstream>
 #include <ios>
diff --git a/tests/std/tests/VSO_0000000_regex_interface/test.cpp b/tests/std/tests/VSO_0000000_regex_interface/test.cpp
index 337415b913..0703637e4b 100644
--- a/tests/std/tests/VSO_0000000_regex_interface/test.cpp
+++ b/tests/std/tests/VSO_0000000_regex_interface/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <regex>
 #include <sstream>
-#include <stdio.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0000000_regex_use/test.cpp b/tests/std/tests/VSO_0000000_regex_use/test.cpp
index 65e792b6d2..f5abd2955e 100644
--- a/tests/std/tests/VSO_0000000_regex_use/test.cpp
+++ b/tests/std/tests/VSO_0000000_regex_use/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdio>
+#include <cstdlib>
 #include <regex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 
 #include <test_regex_support.hpp>
diff --git a/tests/std/tests/VSO_0000000_string_view_idl/test.cpp b/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
index a9d9449915..f8b7b27f2d 100644
--- a/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
+++ b/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
@@ -3,7 +3,7 @@
 
 #define _CONTAINER_DEBUG_LEVEL 1
 
-#include <stddef.h>
+#include <cstddef>
 #include <string_view>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp b/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
index b6fefa1eca..d6c36d48ae 100644
--- a/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
+++ b/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <fstream>
 #include <ios>
 #include <iterator>
diff --git a/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp b/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
index d482bb4c6a..2c436aafeb 100644
--- a/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
+++ b/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <new>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp b/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
index 8a189dacc3..05f87751f8 100644
--- a/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
+++ b/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <exception>
 #include <stdexcept>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp b/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
index a4c11a09a2..b70947cf88 100644
--- a/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
+++ b/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cinttypes>
 #include <cmath>
-#include <inttypes.h>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <limits>
 #include <map>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0102478_moving_allocators/test.cpp b/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
index 14b5809fe3..c11a47b51b 100644
--- a/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
+++ b/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
@@ -4,8 +4,9 @@
 #define _USE_HETEROGENEOUS_ALLOCATOR_COMPARE_IN_INTERNAL_CHECK
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -16,7 +17,6 @@
 #include <regex>
 #include <set>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
index 3b2b36556e..1b1d7d23ef 100644
--- a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
+++ b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <exception>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
index 8046a6088d..de2c60e1bd 100644
--- a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
+++ b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
 #include <exception>
 #include <excpt.h>
-#include <stdint.h>
-#include <stdio.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp b/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
index 2884e162cb..563fd1401a 100644
--- a/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
+++ b/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp b/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
index 3ce1d2604a..e1f550f2fa 100644
--- a/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
+++ b/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 
 using std::max;
 using std::min;
diff --git a/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp b/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
index 0e1e96bb23..77be49b3f5 100644
--- a/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
+++ b/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
@@ -4,13 +4,13 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <cwctype>
 #include <experimental/filesystem>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
-#include <wctype.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp b/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
index 5dd49e8ea5..b5d32c1fce 100644
--- a/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
+++ b/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
+#include <cstddef>
 #include <iterator>
-#include <stddef.h>
 #include <type_traits>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp b/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
index 17bfccdd15..aef6e39bc2 100644
--- a/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
+++ b/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp b/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
index 9b41572560..d39ac22c1a 100644
--- a/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
+++ b/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <utility>
 
diff --git a/tests/std/tests/VSO_0144114_sleep_until/test.cpp b/tests/std/tests/VSO_0144114_sleep_until/test.cpp
index 5c36b9ca81..9c245daf55 100644
--- a/tests/std/tests/VSO_0144114_sleep_until/test.cpp
+++ b/tests/std/tests/VSO_0144114_sleep_until/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <ratio>
 #include <thread>
diff --git a/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp b/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
index d4ac27c874..d66559c658 100644
--- a/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
+++ b/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
-#include <assert.h>
+#include <cassert>
 #include <hash_map>
 #include <hash_set>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp b/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
index 5a81f5cdc6..1d5d69fffc 100644
--- a/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
+++ b/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <system_error>
 
 int main() {
diff --git a/tests/std/tests/VSO_0174871_string_replace/test.cpp b/tests/std/tests/VSO_0174871_string_replace/test.cpp
index 655be2763f..e06149b2ef 100644
--- a/tests/std/tests/VSO_0174871_string_replace/test.cpp
+++ b/tests/std/tests/VSO_0174871_string_replace/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <stdexcept>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp b/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
index df2b3320f0..9ebd654925 100644
--- a/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
+++ b/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
@@ -11,7 +11,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <iterator>
 #include <string>
diff --git a/tests/std/tests/VSO_0180469_fill_family/test.cpp b/tests/std/tests/VSO_0180469_fill_family/test.cpp
index 6c3bef212b..52bc0a41a5 100644
--- a/tests/std/tests/VSO_0180469_fill_family/test.cpp
+++ b/tests/std/tests/VSO_0180469_fill_family/test.cpp
@@ -9,12 +9,12 @@
 // Note that this test *should* trigger 4365 inside STL headers, because it
 // calls std::fill and std::uninitialized_fill with (signed*, signed*, unsigned)
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cmath>
 #include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <memory>
-#include <stdio.h>
-#include <stdlib.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp b/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
index 7c891d41fe..45f422af1a 100644
--- a/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
+++ b/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <iterator>
 #include <limits>
 #include <numeric>
 #include <random>
-#include <stdint.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp b/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
index 3ac82dd4ae..80facce269 100644
--- a/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
+++ b/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <new>
 #include <scoped_allocator>
diff --git a/tests/std/tests/VSO_0226079_mutex/test.cpp b/tests/std/tests/VSO_0226079_mutex/test.cpp
index c23eace460..433e2bb9a2 100644
--- a/tests/std/tests/VSO_0226079_mutex/test.cpp
+++ b/tests/std/tests/VSO_0226079_mutex/test.cpp
@@ -1,13 +1,13 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <mutex>
 #include <shared_mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
 #include <thread>
diff --git a/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp b/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
index 245fcd5aac..2bacb2b91a 100644
--- a/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
+++ b/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <iostream>
 #include <limits>
 #include <locale>
 #include <sstream>
-#include <stdint.h>
 #include <string>
 #include <type_traits>
 
diff --git a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
index cc58553189..91aee8682f 100644
--- a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
+++ b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstddef>
 #include <iterator>
-#include <stddef.h>
 
 #include <test_death.hpp>
 
diff --git a/tests/std/tests/VSO_0397980_codecvt_length/test.cpp b/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
index e1d23def99..7558dc5f4e 100644
--- a/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
+++ b/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
@@ -7,7 +7,7 @@
 #undef _ENFORCE_FACET_SPECIALIZATIONS
 #define _ENFORCE_FACET_SPECIALIZATIONS 0
 
-#include <assert.h>
+#include <cassert>
 #include <codecvt>
 #include <cstdlib>
 #include <iterator>
diff --git a/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp b/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
index dd2d14c1e3..238419a844 100644
--- a/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
+++ b/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <forward_list>
 #include <hash_map>
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
index 0cfde34d7b..e516b792c4 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
index 59087b8cc3..949a61e0aa 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
index 48709db21a..065d264fde 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp b/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
index e27e5da1b8..248d7f995b 100644
--- a/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
+++ b/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0599804_seekg_zero/test.cpp b/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
index a8f5bac24d..af29247ed2 100644
--- a/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
+++ b/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp b/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
index 6c74f6f056..a0a21f4aaa 100644
--- a/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
+++ b/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
@@ -3,15 +3,15 @@
 
 #define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <clocale>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <exception>
 #include <fstream>
 #include <iostream>
-#include <locale.h>
 #include <locale>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp b/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
index 8c32e486ad..95252f6cde 100644
--- a/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
+++ b/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <random>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp b/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
index 1340810482..16d56d315d 100644
--- a/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
+++ b/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <stdexcept>
-#include <stdlib.h>
 #include <vector>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp b/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
index dcc4b80079..aab90b9a5e 100644
--- a/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
+++ b/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <fstream>
 #include <numeric>
-#include <stdio.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp b/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
index 435eac0713..6896543ad3 100644
--- a/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
+++ b/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <unordered_set>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp b/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
index 352e6a7fc6..d0050dba5c 100644
--- a/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
+++ b/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
-#include <stdio.h>
+#include <cassert>
+#include <cstdio>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp b/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
index 9fb4e1553f..c2a56c6e1a 100644
--- a/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
+++ b/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <unordered_set>
 
diff --git a/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp b/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
index 06d4b746ee..afbd1e2ec1 100644
--- a/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
+++ b/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
@@ -4,8 +4,8 @@
 #define _CONTAINER_DEBUG_LEVEL 1
 
 #include <array>
+#include <cstddef>
 #include <deque>
-#include <stddef.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp b/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
index 407f0c7ae3..3bd6487076 100644
--- a/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
+++ b/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <map>
 #include <utility>
diff --git a/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp b/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
index 800628bed6..b7bfceefc9 100644
--- a/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
+++ b/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _STL_INTERNAL_CHECK_EXHAUSTIVE
-#include <assert.h>
+#include <cassert>
+#include <climits>
+#include <cstdlib>
 #include <functional>
 #include <iterator>
-#include <limits.h>
 #include <memory>
 #include <stdexcept>
-#include <stdlib.h>
 #include <type_traits>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp b/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
index 7d9d07627f..db91e58c62 100644
--- a/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
+++ b/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdio>
 #include <experimental/generator>
 #include <future>
 #include <optional>
-#include <stdio.h>
 #include <vector>
 
 using namespace std::experimental;
diff --git a/tools/validate/validate.cpp b/tools/validate/validate.cpp
index 8f41743d7c..6b04580856 100644
--- a/tools/validate/validate.cpp
+++ b/tools/validate/validate.cpp
@@ -4,11 +4,11 @@
 #define _CRT_SECURE_NO_WARNINGS
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
 #include <filesystem>
-#include <stdarg.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <string_view>
 #include <utility>