Stack using Linked List

#include <stdio.h>
#include <stdlib.h>
struct stack{
    int data;
    struct stack *bottom;
}*top = NULL;
void push(int value){//value is to be inserted in the stack
    struct stack *newNode = (struct stack *)malloc(sizeof(struct stack));//memory for new node
    newNode->data = value; newNode->bottom = NULL;//assign values to new node
    if(top) newNode->bottom = top;//if stack is not empty, newNode's bottom points where top points
    top = newNode;//top points to the new node
}
void pop(){
    struct stack *target = top;//target is the top-most element in the stack
    top = top->bottom;//top points to the bottom element in the stack
    free(target);//target is freed as it's no longer needed
}
void display(){
    if(!help)printf("\nStack is Empty!\n");
    else{
        struct stack *help = top;
        while(help){
            printf("\t%d\n",help->data);
            help = help->bottom;
        }
    }
}
int main()
{
    int n;
    while(1){
        display();
        printf(" \n1. Push 2. Pop 3. Exit\n");
        printf(" \nChoose Option: ");
        scanf("%d", &n);
        switch(n){
        case 1:
            printf("\nEnter an integer to push onto the Stack: ");
            scanf("%d",&n);
            push(n);
            break;
        case 2:
            if(top)   pop();
            break;
        case 3:
            printf("\nMore programs @ pastebin.com/u/shailrshah\n");
            return 0;
        default:
            printf("\nInput Error. Try again.");
    }
  }
}