MIT-Curricular/DS/C/Lab/Week6/PrefixCheck.c

#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 stack[top--];
}

int isOperator(char c)
{
    return (c == '+' || c == '-' || c == '*' || c == '/');
}

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

int evaluatePrefix(char *expr)
{
    int len = strlen(expr);
    for (int i = len - 1; i >= 0; i--)
    {
        if (isDigit(expr[i]))
        {
            push(expr[i] - '0');
        }
        else if (isOperator(expr[i]))
        {
            int operand1 = pop();
            int operand2 = pop();
            switch (expr[i])
            {
            case '+':
                push(operand1 + operand2);
                break;
            case '-':
                push(operand1 - operand2);
                break;
            case '*':
                push(operand1 * operand2);
                break;
            case '/':
                if (operand2 != 0)
                    push(operand1 / operand2);
                else
                {
                    printf("Error: Division by zero\n");
                    return -1;
                }
                break;
            }
        }
    }
    return pop();
}

int main()
{
    char expr[MAX_SIZE];
    printf("Enter prefix expression: ");
    gets(expr);

    int result = evaluatePrefix(expr);
    if (result != -1)
    {
        printf("Result: %d\n", result);
    }

    return 0;
}