#ifndef GLIST_H
#define GLIST_H
#include <iostream.h>
// objects of class "block"  are  the building  blocks of a list .
// each block has an information inside it ,prev  and next pointers.
class block  {
public:
   block* next;
   block* prev;
   block(){ next=NULL; prev=NULL; }
   virtual void show()=0;
   virtual void change(char* str)=0;
   void AddAfter(block* Nblock)
       {  next=Nblock; Nblock->prev=this; }
   void AddBefore(block* Nblock)
       { prev=Nblock; Nblock->next =this; }
   block*  GetNext()        { return next; }
   block*  GetPrevious()    { return prev; }
   virtual void    Clear()=0;
   };


class list {
protected:
  block *root ;
  block *tail ;
  long   size;
public:
  list();
  ~list();
  void    AddToEnd(block *Nblock);
  void    AddToFront(block *Nblock);
  block*  GetFirst() { return root; }
  block*  GetLast()  { return tail; }
  long    Size()     { return size; }
  void    Clear();  
  virtual int   del();
  virtual void  print();
  void          print_i(int i);
  block*        return_i(int i);
};




#endif