Stack

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

struct stack {
     int *a;
     int top;
     int maxSize;
};
void initstack(struct stack *p, int maxSize);
void push(struct stack *p, int item);
void display(struct stack p);
int pop(struct stack *p);
void printMenu();

int main() {
     struct stack p;
     int data,ch, data1, m;
     printf("Enter the maximum size of the stack\n");
     scanf("%d",&m);
     initstack(&p,m);
     if(p.a != NULL) {
       do {
         printMenu();
         printf("Enter your choice\n");
         scanf("%d",&ch);
         switch(ch) {
              case 1:
              printf("Enter the element to be pushed\n");
              scanf("%d",&data);
              push(&p, data);
              break;

              case 2:
              data1 = pop(&p);
              if(data1 != -1000)
                printf("The popped element is %d\n",data1);
              break;

              case 3:
              printf("The contents of the stack are ");
              display(p);
              printf("\n");
              break;

              default:
              free(p.a);
              return 0;
           }
         } while(1);
    }
    return 0;
}

void printMenu() {
  printf("Choice 1 : Push\n");
  printf("Choice 2 : Pop\n");
  printf("Choice 3 : Display\n");
  printf("Any other choice : Exit\n");
}

void initstack(struct stack *p, int maxSize) {
  p->top = -1;
  p->maxSize = maxSize;
  p->a = malloc(maxSize * sizeof(int));
}

void push(struct stack *p, int item) {
  if(p->top < p->maxSize-1) {
    p->a[++p->top] = item;
  } else {
      printf("Stack is full\n");
  }
}

void display(struct stack p) {
  int i = 0;
  if(p.top == -1) {
    printf("{}");
  }
  for (; i <= p.top; ++i) {
    printf("%d  ", p.a[i]);
  }
}

int pop(struct stack *p) {
    if(p->top == -1) {
      printf("Stack is empty\n");
      return -1000;
    }
    return p->a[p->top--];
}