Another Program for PUSH and POP operations in a Stack using Arrays in C

#include <stdio.h>
#include<conio.h>
#define MAX 5
int top, flag;


void push (int s[], int data)
{   if (top == (MAX-1))
 flag = 0;
    else
    {   flag = 1;
 ++top;
 s [top] = data;
    }
}
 

int pop (int s[])
{  
    int ret;
    if (top == -1)
    {   ret = 0;
 flag = 0;
    }
    else
    {   flag = 1;
 ret = s [top];
 --top;
    }
return ret;
}


void display (int s[])
{   int i;
    printf ("\nThe s is: ");
    if (top == -1)
 printf ("empty");
    else
    {   for (i=top; i>=0; --i)
    printf ("\n--------\n|%3d   |\n--------",s[i]);
    }
    printf ("\n");
}
 

void main()
{  
    int s [MAX], data;
    int ch;
    clrscr ();
    top = -1;
 
    do
    {  do
       {   printf ("\nMAIN MENU");
    printf ("\n1.PUSH (Insert) into the s");
    printf ("\n2.POP  (Delete) from the s");
    printf ("\n3.Exit.");
    printf ("\nEnter Your Choice:  ");
    scanf  ("%d", &ch);
    if (ch<1 || ch>3)
        printf ("\nInvalid Choice, Please try again");
 }while (ch<1 || ch>3);
       switch (ch)
       {case 1:
  printf ("\nEnter the Element to be pushed : ");
  scanf  ("%d", &data);
  printf (" %d", data);
  push (s, data);
  if (flag)
  {   printf ("\nAfter Pushing ");
      display (s);
      if (top == (MAX-1))
   printf ("\nThe s is Full");
  }
  else
      printf ("\ns overflow on Push");
  break;
       case 2:
  data = pop (s);
  if (flag)
  {    printf ("\nThe Popped data is %d.  After Popping: ");
       display (s);
  }
  else
       printf ("\ns underflow on Pop");
  break;
       default:
  printf ("\nEnd.");
       }
    }while (ch != 3);
getch();
}