Stack operations(basic) in C

stack.c

/**
  * A Stack is a last in, first out (LIFO) abstract data type and data
  * structure.It is characterized by three fundamental operations: push,
  * pop and stack top.

  * PUSH :  The push operation adds a new item to the top of the stack, or
  * initializes the stack if it is empty, but if the stack is full and
  * does not contain more space to accept the given item it is considered
  * as an Overflow state (It means that the stack is overloaded or no more
  * space for new item).

  * POP :  The pop operation removes an item from the top of the stack,
  * but if the stack is empty then it goes into underflow state (It means
  * no items are present in the stack to be removed).

  * STACK TOP :  The stack top operation gets the data from the top-most
  * position and returns it to the user without deleting it. The same
  * underflow state can also occur in stack top operation if stack is empty.
  **/

#include<stdio.h>
#define MAX 50

int main()
{
  int stack[MAX], top = -1, e;
  int choice;
  void PUSH(int *, int, int *);
  void POP(int *, int *);
  void DISPLAY_TOP(int *, int *);

  while(1) {
    printf("\nMenu\n1.PUSH\n2.POP\n3.DISPLAY STACK TOP\n4.EXIT\n");
    printf("Type 1 to Push, 2 to Pop, 3 to display and 4 to Exit : \n");
    scanf("%d", &choice);
    switch(choice) {
    case 1:
      printf("Enter element to be pushed : \n");
      scanf("%d", &e);
      PUSH(stack, e, &top);
      break;
    case 2:
      POP(stack, &top);
      break;
    case 3:
      DISPLAY_TOP(stack, &top);
      break;
    case 4:
      exit(0);
    default:
      printf("Invalid entry!!\n");
    }
  }

  return 0;
}

void PUSH(int *stack, int item, int *top)
{
  if((*top) == MAX - 1) {
    printf("Stack Overflow!\n");
    return;
  } else {
    stack[++(*top)] = item;
    printf("%d inserted\n", item);
  }
}

void POP(int *stack, int *top)
{
  int item;

  if((*top) == -1) {
    printf("Stack underflow\n");
  } else {
    item = stack[(*top)];
    printf("Popped item : %d\n", item);
    (*top)--;
  }
}

void DISPLAY_TOP(int *stack, int *top)
{
  int i;
  if(*top == -1)
    printf("Stack underflow\n");
  else {
    printf("The stack contents are :\n");
    for(i = 0; i <= (*top); i++)
      printf("%d ",stack[i]);
    printf("\nThe top of the stack : %d\n", stack[(*top)]);
    printf("\n");
  }
}