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StackCalculator.java
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StackCalculator.java
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import java.util.Scanner;
import java.util.Stack;
public class StackCalculator {
// method to evaluate the postfix expression
public static int evaluatePostfix(String postfix) {
Stack<Integer> stack = new Stack<Integer>();
boolean prevNeg = false;
String temp = "";
for (int i = 0; i < postfix.length(); i++) {
char ch = postfix.charAt(i);
if (Character.isDigit(ch)) {
if (prevNeg) {
//stack.push(-ch + '0');
temp = "-"+ch;
prevNeg = false;
} else {
temp = temp + ch;
}
//stack.push(ch + '0');
} else if (ch == '^') { // treating ^ as negative sign
//stack.push(-stack.pop());
prevNeg = !prevNeg;
} else if (ch == ',') {
if (!temp.equals(""))
stack.push(Integer.parseInt(temp));
temp = "";
} else {
if (!temp.equals("")) {
stack.push(Integer.parseInt(temp));
temp = "";
}
int num2 = stack.pop();
int num1 = stack.pop();
switch (ch) {
case '+':
byte sum = (byte) (num1 + num2);
if ((num1 > 0 && num2 > 0 && sum < 0) || (num1 < 0 && num2 < 0 && sum > 0)) {
System.out.println("Overflow occurred during addition");
}
stack.push((int)sum);
break;
case '-':
byte difference = (byte) (num1 - num2);
if ((num1 > 0 && num2 < 0 && difference < 0) || (num1 < 0 && num2 > 0 && difference > 0)) {
System.out.println("Overflow occurred during subtraction");
}
stack.push((int)difference);
break;
case '*':
int product = (int)(num1 * num2);
if (product > Byte.MAX_VALUE || product < Byte.MIN_VALUE)
System.out.println("Overflow occurred during subtraction");
byte byProduct = (byte) product;
stack.push((int)(byProduct));
break;
case '/':
int quotient = (int)Math.round((double) num1 / (double) num2);
byte byQuotient = (byte) quotient;
stack.push((int) byQuotient);
break;
}
}
}
if (stack.isEmpty() && !temp.equals(""))
stack.push(Integer.parseInt(temp));
return stack.pop();
}
public static String infixToPostfix(String infix) {
Stack<Character> stack = new Stack<Character>();
Stack<Integer> stackInt = new Stack<Integer>();
StringBuilder postfix = new StringBuilder();
char prev = 0;
for (int i = 0; i < infix.length(); i++) {
char ch = infix.charAt(i);
if (ch == '(') {
stack.push(ch);
} else if (ch == ')') {
while (!stack.isEmpty() && stack.peek() != '(') {
postfix.append(stack.pop());
}
stack.pop();
} else if (Character.isDigit(ch)) {
postfix.append(ch);
} else if (ch == '-' && (prev == 0 || prev == '(')) {
postfix.append('^');
} else {
while (!stack.isEmpty() && getPrecedence(ch) <= getPrecedence(stack.peek())) {
postfix.append(stack.pop());
}
stack.push(ch);
postfix.append(',');
}
prev = ch;
}
while (!stack.isEmpty()) {
postfix.append(stack.pop());
}
return postfix.toString();
}
public static int getPrecedence(char operator) {
switch (operator) {
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
case '^': // treating ^ as negative sign
return 3;
default:
return -1;
}
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter an arithmetic expression in infix notation: ");
String infix = scanner.nextLine();
String postfix = infixToPostfix(infix);
int result = evaluatePostfix(postfix);
System.out.println("Postfix expression: " + postfix.replaceAll(",",""));
System.out.println("Result: " + result);
}
}