Stack data structure using linked list in C programming with menu

// stack using linked list
#include <stdio.h>
#include <stdlib.h>


struct stackItem
{
    int data;
    struct stackItem *next;
};

struct stackItem *top = NULL;


void push(int value)
{
    struct stackItem * node = (struct stackItem *)malloc(sizeof(struct stackItem));
    node->data = value;
    node->next = top;
    top = node;
    
    /*
    if(top == NULL)
    {
        node->next = NULL;
        top = node;
    }
    else
    {
        node->next = top;
        top = node;
    }
    */
    printf("Pushing: %d. Done", node->data);
}

void display()
{
    struct stackItem *c;
    c = top;  
    if(top == NULL)
    {
        printf("nStack is empty");
        return;
    }
        
    while(c != NULL)
    {
        printf("n%d", c->data);
        c = c->next;
    }
}//display()

int pop()
{
    struct stackItem *poppednode;
    int v;
    if(top == NULL)
    {
        // Stack is empty
        return -999;
    }
    else
    {
        poppednode = top;
        v = poppednode->data;
        top= top->next;
        free(poppednode);    
        
        return v;    
    }    
}//pop()

int peek()
{
    int v;
    
    if(top == NULL)
    {
        // Stack is empty
        return -999;
    }
    else
    {
        v = top->data;
        return v;    
    }        
}

void deleteStack()
{
    struct stackItem *c;
    while(top != NULL)
    {
        c = top;
        top = top->next;
        free(c);
    }
    printf("nAll nodes freed...");
    display();
}

void main()
{
    int option, val;
    
    do
    {
        printf("n *****MENU*****");
        printf("n 1. PUSH");
        printf("n 2. POP");
        printf("n 3. PEEK");
        printf("n 4. DISPLAY");
        printf("n 0. EXIT");
        printf("n Enter your choice: ");
        scanf("%d",&option);
        
        switch(option)
        {
            case 1:
                printf("n Enter the value to push on Stack: ");
                scanf("%d",&val);
                push(val);
                break;
                
            case 2:
                val = pop();
                
                if(val!=-999)
                    printf("n The value popped from Stack = %d", val);
                break;
                
            case 3:
                val = peek();
                if(val!=-999)
                    printf("n The value at top of Stack = %d", val);    
                break;
            
            case 4:
                printf("n The contents of Stack are : n");
                display();
                break;
                
            case 0:
                printf("nFreeing Memory...");
                deleteStack();
                printf("nExiting...");
                exit(0);
                break;
            default:
                printf("nInvalid option. Try again...");                
        }
        
    }while(1);
            
    getch();
}