Stack c program

#include <stdio.h>

#define MAXSIZE 5

struct stack {
    int stk[MAXSIZE];
    int top;
};
typedef struct stack STACK;
STACK s;

void push(void);

int pop(void);

void display(void);

int main()
{
    int choice;
    int option = 1;
    s.top = -1;

    printf("STACK OPERATION\n");
    printf("------------------------------------------\n");
    printf("1 --> PUSH\n");
    printf("2 --> POP\n");
    printf("3 --> DISPLAY\n");
    printf("4 --> EXIT\n");
    printf("------------------------------------------\n");
    while (option != 4)
    {
        printf("Enter your choice : ");
        scanf("%d", &choice);
        switch (choice)
        {
            case 1:
                push();
                break;
            case 2:
                pop();
                break;
            case 3:
                display();
                break;
            case 4:
                return 0;
        }
    }
    return 0;
}

void push()
{
    int num;
    if (s.top == (MAXSIZE - 1))
    {
        printf("Stack is Full\n");
        return;
    }
    else
    {
        printf("Enter the element to be pushed : ");
        scanf("%d", &num);
        s.top = s.top + 1;
        s.stk[s.top] = num;
    }
    return;
}

int pop()
{
    int num;
    if (s.top == -1)
    {
        printf("Stack is Empty\n");
        return (s.top);
    }
    else
    {
        num = s.stk[s.top];
        printf("Poped element is = %d\n", s.stk[s.top]);
        s.top = s.top - 1;
    }
    return (num);
}

void display()
{
    int i;
    if (s.top == -1)
    {
        printf("Stack is empty\n");
        return;
    }
    else
    {
        printf("\nThe status of the stack is \n");
        for (i = s.top; i >= 0; i--)
        {
            printf("%d\n", s.stk[i]);
        }
    }
    printf("\n");
}

Output : 

STACK OPERATION
------------------------------------------
1 --> PUSH
2 --> POP
3 --> DISPLAY
4 --> EXIT
------------------------------------------
Enter your choice : 1
Enter the element to be pushed : 12
Enter your choice : 1
Enter the element to be pushed : 23
Enter your choice : 1
Enter the element to be pushed : 34
Enter your choice : 2
Poped element is = 34
Enter your choice : 3

The status of the stack is 
23
12

Enter your choice : 4