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

#define MAX_SIZE 100

int stack[MAX_SIZE];
int top = -1;

void push(int item) {
    if (top >= MAX_SIZE - 1) {
        printf("Stack Overflow\n");
        return;
    }
    stack[++top] = item;
}

int pop() {
    if (top < 0) {
        printf("Stack Underflow\n");
        return -1;  // Return a sentinel value instead of exiting
    }
    return stack[top--];
}

int isDigit(char c) {
    return c >= '0' && c <= '9';
}

int evaluatePostfix(char* exp) {
    int i, operand1, operand2, result;
    
    for (i = 0; exp[i] != '\0'; i++) {
        if (isDigit(exp[i])) {
            push(exp[i] - '0');
        } else {
            operand2 = pop();
            operand1 = pop();
            switch (exp[i]) {
                case '+': push(operand1 + operand2); break;
                case '-': push(operand1 - operand2); break;
                case '*': push(operand1 * operand2); break;
                case '/': 
                    if (operand2 == 0) {
                        printf("Error: Division by zero\n");
                        return -1;  // Return a sentinel value instead of exiting
                    }
                    push(operand1 / operand2); 
                    break;
            }
        }
    }
    return pop();
}

int main() {
    char exp[MAX_SIZE];
    printf("Enter a postfix expression: ");
    fgets(exp, MAX_SIZE, stdin);
    exp[strcspn(exp, "\n")] = 0;  // Remove newline if present
    
    int result = evaluatePostfix(exp);
    if (result != -1) {
        printf("Result: %d\n", result);
    }
    return 0;
}