1// Aim: Program to perform Postfix Evaluation.
2#include<stdio.h>
3#include<stdlib.h>
4#include<ctype.h>
5
6int stack[20];
7int top = -1;
8
9void push(int x) {
10    stack[++top] = x;
11}
12
13int pop() {
14    return stack[top--];
15}
16
17int evaluatePostfix(char* postfix) {
18    int i;
19    char symbol;
20    int op1, op2;
21
22    for(i = 0; postfix[i] != '\0'; i++) {
23        symbol = postfix[i];
24        if(isdigit(symbol)) {
25            push(symbol - '0');
26        } else {
27            op2 = pop();
28            op1 = pop();
29            switch(symbol) {
30                case '+': push(op1 + op2); break;
31                case '-': push(op1 - op2); break;
32                case '*': push(op1 * op2); break;
33                case '/': push(op1 / op2); break;
34            }
35        }
36    }
37    return pop();
38}
39
40int main() {
41    char postfix[20];
42    printf("Enter the postfix expression\n");
43    scanf("%s", postfix);
44
45    int result = evaluatePostfix(postfix);
46    printf("Postfix expression is %s\n", postfix);
47    printf("Evaluation result is %d\n", result);
48
49    return 0;
50}