Add example that read from stdin

stdin_ex.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(int argc, char *argv[]) {  
+  // create a buffer that can hold
+  // up to 255 characters
+  char buf[];
+  buf = "Hello";
+  char buffer[256];
+
+
+  // read one line at a time and send it to calc function for processing
+  while(1) {
+	  char *s;
+	  char op;
+	  float x, y;
+	  fscanf(stdin, "%c %f %f", &op, &x, &y);
+	  switch (op) {
+		case '+' : printf("%.2f\n", x + y); break;
+		case '-' : printf("%.2f\n", x - y); break;
+		case 'x' : printf("%.2f\n", x * y); break;
+		case '/' : printf("%.2f\n", x / y); break;
+	  }
+  }
+
+  /*
+  while ((s = fgets(buffer, 255, stdin)) != NULL) {
+    float ans = calc(buffer);
+    printf("%.2f\n", ans);
+  }
+  */
+  return 0;
+}