////   This file contains the C++ code from Program A.8 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm0A_08.cpp//class Point{    int x;    int y;public:    Point (int, int);    // ...};class GraphicalObject{protected:    Point center;    GraphicalObject (Point const& p) :	center (p) {}public:    virtual ~GraphicalObject ();    virtual void Draw () const = 0;    virtual void Erase () const;    virtual void MoveTo (Point const&);};