#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";
}

/* -----------------------------------------------------------
   ----------------------------------------------------------- */
void DeleteNeg(ListElem * & head)
{
   ListElem *p1, *p2;

   if ( head == NULL )
   {
      head = NULL;
   }
   else
   {
      if ( head->value < 0 )
      {
            p2 = head;
            head = head->next;

            delete p2;           // Deallocate space
      }
      else
      {
         p1 = head;  
         p2 = head->next;    

         while ( p2 != NULL && p2->value >= 0 )    
         {
            p1 = p2; 
            p2 = p2->next;   
         }

         p1->next = p2->next;
         delete p2;             // Deallocate space
      }
   }
}


/* -----------------------------------------------------------
   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
}




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

   p = new ListElem;
   p->value = 4500;
   InsertAtHead(head, p);
   Print(head);

   p = new ListElem;
   p->value = -5500;
   InsertAtHead(head, p);
   Print(head);

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

   DeleteNeg(head);
   Print(head);

   DeleteNeg(head);
   Print(head);

   DeleteNeg(head);
   Print(head);
}