Stack implementation using Linked List

#include <iostream>
using namespace std;


//Node structure created
struct Node 
{
   int data;
   struct Node *next;
};

struct Node* top = NULL;        //Top initialized as NULL, initially empty

void push(int a)                // To add elements to the stack
{
   struct Node* newnode = new Node();
   newnode->data = a;
   newnode->next = top;
   top = newnode;
}

void pop()                      // To delete elements from the stack
{
   if(top==NULL)
   {
        cout<<"Stack is already empty!..."<<endl;
   }
   else 
   {
      cout<<"The popped element:"<< top->data<<endl;
      top = top->next;
   }
}

void display()                  // To display elements of the stack
{
   struct Node* temp;
   if(top==NULL)
   {
        cout<<"Stack is empty!";
   }
   else 
   {
      temp = top;
      cout<<"Elements are:";
      while (temp!=NULL) 
      {
         cout<< temp->data <<"->";
         temp = temp->next;
      }
   }
   cout<<endl;
}

//Main program
int main() 
{
   int c, a;
   cout<<"Options are:"<<endl;
   cout<<"1. Push  2. Pop  3. Display  4.Exit"<<endl;
   do {
      cout<<"Enter choice: "<<endl;
      cin>>c;
      switch(c)                             //switch case to implement user choice based operation implementation 
      {
         case 1: {
                    cout<<"Enter value:"<<endl;
                    cin>>a;
                    push(a);
                    break;
                 }
         case 2: {
                    pop();
                    break;
                 }
         case 3: {
                    display();
                    break;
                 }
         case 4: {
                    cout<<"Exiting the program....."<<endl;
                    break;
                 }
         default:{
                    cout<<"Wrong Choice"<<endl;
                 }
      }
   }while(c!=4);                        //exit condition
   return 0;
}