#include <iostream.h>

class ListElem
{
public:
   int      value;      // Integer
   ListElem *next;      // Pointer used to make link    
};


void Print(ListElem *head)
{
   ListElem *p;

   p = head;             // Very important: start at first element

   cout << "List ==> ";
   while ( p != NULL )
   {
      cout << p->value << "  ";  // Access value stored in list element  
      p = p->next;               // Visit next element in list
   }
   cout << "\n\n";
}



/* -----------------------------------------------------------
   DeleteAtTail: Delete elem at TAIL of linked list
   ----------------------------------------------------------- */
ListElem * DeleteAtTail(ListElem * head)
{
    ListElem *p2;
    ListElem *p1;

    if ( head == NULL ) // Delete only from non-empty list
    {
       return(NULL);
    }
    else
    {
       if ( head->next == NULL )
       {  // Handle special case: List has 1 element

	  delete head;	    // Deallocate space

	  return(NULL);
       }
       else
       {  // The general case

	  // Find the last-but-one "p1" and last "p2" elements

	  p1 = head;
	  p2 = head->next;

	  while ( p2->next != NULL )
	  {
	     p1 = p2;
	     p2 = p2->next;
	  }

	  p1->next = NULL;   	// Delete element following list
	  delete p2;		// Deallocate space

	  return(head);
       }

    }
}


/* -----------------------------------------------------------
   InsertAtHead: insert elem at start of linked list
		 Function returns head of new linked list
   ----------------------------------------------------------- */
ListElem * InsertAtHead(ListElem * head, ListElem * elem)
{
   elem->next = head;    // Make new list element points   
                         // to the start of "old list"   

   return(elem);	 // Return the new head
}

int main(int argc, char *argv[])
{
   ListElem *head, *p;
   void Print(ListElem *);
   extern ListElem *InsertAtHead(ListElem *, ListElem *);
   extern ListElem * DeleteAtTail(ListElem * head);

   head = NULL;
   Print(head);

   p = new ListElem;
   p->value = 1500;
   head = InsertAtHead(head, p);
   Print(head);
   
   p = new ListElem;
   p->value = 2500;
   head = InsertAtHead(head, p);
   Print(head);
   
   p = new ListElem;
   p->value = 3500;
   head = InsertAtHead(head, p);
   Print(head);

   // ========================================== Removing...

   head = DeleteAtTail(head);
   Print(head);

   head = DeleteAtTail(head);
   Print(head);

   head = DeleteAtTail(head);
   Print(head);

   head = DeleteAtTail(head);
   Print(head);
}