postfix evaluation

#include<stdio.h>
#include<math.h>
#define MAX 80

struct stack
{
    int data[MAX];
    int top;
};
typedef struct stack STACK;
STACK s;

int isEmpty()
{
    if(s.top == -1)
        return 1;
    else
        return 0;
}

int isFull()
{
    if(s.top == MAX - 1)
        return 1;
    else 
        return 0;
}

void push(int num)
{
    if(isFull())
        printf("The stack is full\n");
    else
    {
        s.top++;
        s.data[s.top] = num;
    }
    
}

int pop()
{
    int x;
    if(isEmpty())
        printf("The stack is empty\n");
    else
    {
        x = s.data[s.top--];
        return x;
    }

}

int gettype(char t)
{
    switch(t)
    {
        case '+':
        case '-':
        case '*':
        case '/':
        case '%':
        case '$':
        case '^': return 2;
        default: return 1;
    }
}

void eval(char op, int num1, int num2)
{
    int result;
    switch(op)
    {
        case '+': result = num1 + num2;
                break;
        case '-': result = num2 - num1;
                break;
        case '*': result = num1*num2;
                break;
        case '/': result = num1/num2;
                break;
        case '%': result = num1%num2;
                break;
        case '$':
        case '^': result = pow(num1, num2);
                break;
    }
    push(result);
}

void main()
{
    char postfix[MAX];
    int i, num1, num2, type, ans, result, ch;
    printf("Enter the postfix expression\n");
    scanf("%s", postfix);
    for(i=0;postfix[i]!='\0';i++)
    {
        type = gettype(postfix[i]);
        switch(type)
        {
            case 1: ch = postfix[i] - '0';
            push(ch);
            break;
            case 2:num1 = pop();
                   num2 = pop();
                   eval(postfix[i], num1, num2);
                   break;

        }
        
        
    }
    result = pop();
    printf("The value of the postfix expression is %d", result);
    
}