#include <stdio.h>
#include <stdlib.h>
#include "stack.h"

void Stack_push(Stack *stack, int element)
{
  stack->ptr++;
  if(stack->ptr == (stack->tos + SIZE)) {
    printf("Stack Overflow.\n");
    exit(1);
  }
  *stack->ptr = element;
}

int Stack_pop(Stack *stack)
{
  if(stack->ptr == stack->tos) {
    printf("Stack Underflow.\n");
    exit(1);
  }
  stack->ptr--;
  return *(stack->ptr + 1);
}

void Stack_add(Stack *stack)
{
  int a = *stack->ptr;
  int b = *(stack->ptr - 1);
  int result = a + b;

  Stack_pop(stack);
  Stack_pop(stack);
  Stack_push(stack, result);
}

void Stack_sub(Stack *stack)
{
  int a = *stack->ptr;
  int b = *(stack->ptr - 1);
  int result = a - b;

  Stack_pop(stack);
  Stack_pop(stack);
  Stack_push(stack, result);
}

void Stack_reset(Stack *stack)
{
  int i = 0;
  for (i = 0; i < SIZE; i++) {
    stack->body[i] = 0;
  }
}