static stack allocation

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX_STACK_SIZE      100
typedef struct{
  int key;
}element;

element stack[MAX_STACK_SIZE];
int top = -1;

bool isEmpty();
bool isFull();
void push(element item);
element pop();
void stackFull();
void stackEmpty();
void stackDisplay();

int main(void)
{
  int selection;
  int tmp;
  int i;
  element tmpItem;

  printf("stack program test\n");
  while(1){
    printf("\n- menu - \n");
    printf("1. push\n");
    printf("2. pop\n");
    printf("3. display\n");
    printf("4. exit\n");
    printf("Select the menu: ");
    scanf("%d", &selection);

    switch(selection){
      case 1:
        printf("Enter the key: ");
        scanf("%d", &tmp);
        tmpItem.key = tmp;
        push(tmpItem);
        break;

      case 2:
        tmpItem = pop();
        printf("Pop the item: %d\n", tmpItem.key);
        break;

      case 3:
        stackDisplay();
        break;

      case 4:
        return 1;

      default:
        printf("you must enter the number listed on menu\n");
        break;
    }
  }
  return 0;
}

bool isEmpty()
{
  return top < 0;
}

bool isFull()
{
  return top >= MAX_STACK_SIZE - 1;
}

void push(element item)
{
  if(top >= MAX_STACK_SIZE -1){
    stackFull();
  }
  stack[++top] = item;
}

element pop()
{
  if(top == -1)
    stackEmpty();
  return stack[top--];
}

void stackFull()
{
  fprintf(stderr, "Stack is full, cannot add element\n");
  exit(EXIT_FAILURE);
}

void stackEmpty()
{
  fprintf(stderr, "Stack is empty, cannot pop element\n");
  exit(EXIT_FAILURE);
}

void stackDisplay()
{
  int i;
  if(isEmpty()) stackEmpty();
  printf("\nstack key list\n");
  for(i = 0; i < top + 1; i++){
    printf("stack[%d] : %d\n", i, stack[i].key);
  }
}