#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";
}

/* -----------------------------------------------------------
   InsertAtHead: insert elem at start of linked list

   Question: what would happen if we pass "head" by value ?
   ----------------------------------------------------------- */
void InsertAtHead(ListElem * & head, ListElem * elem)
{
   elem->next = head;    // Make new list element points   
                         // to the start of "old list"   

   head = elem;          // Make "head" points to 
                         // the **new** starting object
}


/* -----------------------------------------------------------
   DeleteAtTail: Delete elem at TAIL of linked list

   Question: what would happen if we pass "head" by value ?
   ----------------------------------------------------------- */
void DeleteAtTail(ListElem * & head)
{
    ListElem *last;
    ListElem *last_but_one;

    if ( head != NULL ) // Delete only from non-empty list
    {
       if ( head->next == NULL )
       {  // Handle special case: List has 1 element
	  last = head;      // Save for delete operator
	  head = NULL;
	  delete last;	    // Use saved value to delete element
       }
       else
       {  // The general case

	  // Find the "last_but_one" element

	  last_but_one = head;

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

	  // Delete element following the "last_but_one" element    
	  last_but_one->next = NULL;
       }

    }
}




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

   head = NULL;
   Print(head);

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

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

   DeleteAtTail(head);
   Print(head);

   DeleteAtTail(head);
   Print(head);

   DeleteAtTail(head);
   Print(head);

   DeleteAtTail(head);
   Print(head);
}