#include<iostream.h>
#include<conio.h>
 
struct node
{
  int data;
  node *next;
}*p,*front,*rear;
 
void display();
void push(int);
void pop();
int main()
{
  int choice,item;
	while(choice != 4)
	  {
	    cout<<"\n Enter your choice : ";
	    cout<<"\n 1. Push an element into Queue : "
		<<"\n 2. Pop an element. "
		<<"\n 3. Display elements in queue. "
		<<"\n 4. Exit.\n ";
	    cin>>choice;
		switch(choice)
		  {
		  case 1:
		    cout<<"\nEnter the element you want to insert : ";
		    cin>>item;
		    push(item);
		    break;
		  case 2:
		    pop();
		    break;
		  case 3:
		    display();
		    break;
		  case 4:
		    break;
		  default:
		    cout<<"\n Invalid choice.";
		    break;
		  }
	  }
	  getch();
}
 
void push(int x)
{
  if(front==NULL)
    {
      node *q=new node;
      q->data=x;
      q->next=front;
      front=q;
      rear=q;
      front->next=rear;
    }
  else
    {
      node * t= new node;
      t->data=x;
      rear->next=t;
      rear=t;
    }
}
 
 
void display()
{
  cout<<"\n\n The queue is : \n";
  node* temp=new node;
  temp=front;
  if(temp==NULL)
    cout<<"Queue is empty!";
  else
    {
      do
	{
	  cout<<temp->data<<" << ";
     temp=temp->next;
	}
      while(temp!=rear);
if(front!=rear)
  cout<<rear->data;
    }
}
 
void pop()
{
  if(front->next==rear)
    {
      cout<<"\n The Queue is:\n"<<rear->data;
    }
  else
    {
      node* d;
      d=front;
      front=front->next;
      delete d;
    }
}