help me with linked ques

[jasleen12345]

this is a program that my teacher gave me in the class. but i didn't understand it....please explain it to me step by step...

#include<iostream.h>
class queue
{
 int element;
 queue* next;
public:
 queue* enqueue(queue*,int);
 queue* dequeue(queue*);
 void queue_display(queue*);
}*head,*tail,object;

queue* queue::enqueue(queue* head,int key)
{
 queue* temp;
 temp=new queue;
 temp->element=key;
 temp->next=NULL;
 if(head==NULL)
  head=temp;
 else
  tail->next=temp;
 tail=temp;
 return head;
}
queue* queue::dequeue(queue* head)
{
queue* temp;
if(head==NULL)
{
 cout<<"\nit is impossible to dequeue an element as ";
 return NULL;
}
else if(head->next==NULL)
{
 cout<<"\nthe element dequeued from the queue is: "<<head->element<<endl;
 return NULL;
}
else
{
 cout<<"\nthe element dequeued from the queue is "<<head->element<<endl;
 temp=head->next;
 head=temp;
 cout<<"\nthe elements of queue after dequeueing are \n";
 return head;
}
}
void queue::queue_display(queue* head)
{
 if(head!=NULL)
 {
  while(head->next!=NULL)
  {
	cout<<head->element<<"->";
	head=head->next;
  }
  cout<<head->element;
  cout<<endl;
 }
 else
  cout<<"the queue is empty\n";
}
void choice()
{

 int key,ch;
 head=tail=NULL;
 cout<<"\nchoose the operation\n";
 cout<<"\n1.enqueue\t2.dequeue\t3.exit\n\n";
 cin>>ch;
 while(ch!=3)
 {
  switch(ch)
  {
  case 1:
  cout<<"\nenter the key to be inserted\n";
  cin>>key;
  head=object.enqueue(head,key);
  cout<<"\nthe elements of queue after inserting "<<key<<" are\n";
  object.queue_display(head);
  break;
  case 2:
	head=object.dequeue(head);
	object.queue_display(head);
	break;
  case 3:
	break;
  default:
	cout<<"\nenter correct choice\n";
	break;
  }
  cout<<"\n——————————————————————————\n";
 cout<<"\nchoose the operation\n";
 cout<<"\n1.enqueue\t2.dequeue\t3.exit\n\n";
 cin>>ch;

  cout<<"\n——————————————————————————\n";
 }
}
void main()
{
 choice();
}

[Ancient Dragon]

>>#include
>>void main()

Get another teacher because that one doesn't know what he/she's doing. Better yet, go to a different school because that one is probably trying to teach you how to program in the 21st century with a compiler that was written in the 2nd century (e.g. Turbo C++)

But besides that, did you bother to compile and run that program yourself so that you can see what it does? If not then you should do so.