Write a program for postfix evaluation

postfix-eval.c

#include<stdio.h>
#include<conio.h>
#include<string.h>

#define MAX 50
int stack[MAX];
char post[MAX];
int top = -1;
void pushstack(int tmp);
void evaluate(char c);
void main() {
  int i, l;
  printf("Insert a postfix notation :: ");
  gets(post);
  l = strlen(post);
  for (i = 0; i < l; i++) {
    if (post[i] >= '0' && post[i] <= '9') {
      pushstack(i);
    }
    if (post[i] == '+' || post[i] == '-' || post[i] == '*' ||
      post[i] == '/' || post[i] == '^') {
      evaluate(post[i]);
    }
  }
  printf("\n\nResult :: %d", stack[top]);
  getch();
}

void pushstack(int tmp) {
  top++;
  stack[top] = (int)(post[tmp] - 48);
}

void evaluate(char c) {
  int a, b, ans;
  a = stack[top];
  stack[top] = '\0';
  top--;
  b = stack[top];
  stack[top] = '\0';
  top--;
  switch (c) {
  case '+':
    ans = b + a;
    break;
  case '-':
    ans = b - a;
    break;
  case '*':
    ans = b * a;
    break;
  case '/':
    ans = b / a;
    break;
  case '^':
    ans = b ^ a;
    break;
  default:
    ans = 0;
  }
  top++;
  stack[top] = ans;
}

Output