ST8

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
struct Stack
{
    int top;
    unsigned capacity;
    int* array;
};
struct Stack* MakeStack(unsigned capacity)
{
    struct Stack* stack = (struct Stack*) malloc(sizeof(struct Stack));
    if (!stack) return NULL;
    stack->top = -1;
    stack->capacity = capacity;
    stack->array = (int*) malloc(stack->capacity * sizeof(int));
    if (!stack->array) return NULL;
    return stack;
}

int isEmpty(struct Stack* stack)
{
    return stack->top == -1 ;
}
char peek(struct Stack* stack)
{
    return stack->array[stack->top];
}
char pop(struct Stack* stack)
{
    if (!isEmpty(stack))
        return stack->array[stack->top--] ;
    return '$';
}
void push(struct Stack* stack, char op)
{
    stack->array[++stack->top] = op;
}
int evaluatePostfix(char* exp)
{
    struct Stack* stack = MakeStack(strlen(exp));
    int i;
    if (!stack) return -1;
    for (i = 0; exp[i]; ++i)
    {
        if (isdigit(exp[i]))
            push(stack, exp[i] - '0');
        else
        {
            int val1 = pop(stack);
            int val2 = pop(stack);
            switch (exp[i])
            {
             case '+': push(stack, val2 + val1); break;
             case '-': push(stack, val2 - val1); break;
             case '*': push(stack, val2 * val1); break;
             case '/': push(stack, val2/val1);   break;
            }
        }
    }
    return pop(stack);
}
int main()
{
    char exp[100] ;
  fgets(exp,100,stdin);
    printf ("Value of %s is %d", exp, evaluatePostfix(exp));
    return 0;
}