Stack operations using Linked List implementation

#include<iostream>
using namespace std;

 void push();
 void pop();
 void traverse();

 struct node
 { int num;
   struct node *next;
 }*top=NULL;

 typedef struct node node;
 typedef struct node* nptr;

 void main()
 { char choice;
   while(1)
   {
   system("cls");
   cout<<"-----STACK USING LINKED LIST-----\n\n";
   cout<<" 1.PUSH\n";
   cout<<" 2.POP\n";
   cout<<" 3.TRAVERSE\n";
   cout<<" 4.EXIT\n";
   cout<<" Enter your choice: ";
   cin>>choice;
   switch(choice)
   { case '1': push();
      break;
     case '2': pop();
      break;
     case '3': traverse();
      break;
     case '4': exit(0);
     default: cout<<"\n\nInvalid choice\n\n";
   }
   system("pause");
  }
 }

  void push()
  { nptr p;
    int item;
    if((p=new node)!=NULL)
    { cout<<"\n\nEnter the item: ";
      cin>>item;
      p->num=item;
      p->next=top;
      top=p;
    }
    else
    { cout<<"\n\nOverflow\n\n";
    }
  }

  void pop()
  { nptr p;
    if(top==NULL)
    { cout<<"\n\nUNDERFLOW\n\n";
    }
    else
    { p=top;
      top=top->next;
      cout<<"\n "<<p->num<<" is deleted\n\n";
      delete p;
    }
  }

  void traverse()
  { nptr p;
    p=top;
    if(top==NULL)
    { cout<<"\n stack is empty\n\n";
    }
    else
    { cout<<"\n\n STACK: ";
      while(p!=NULL)
      { cout<<" "<<p->num;
p=p->next;
      }
    }
cout<<"\n\n";
  }