////   This file contains the C++ code from Program 7.19 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/pgm07_19.cpp//class Polynomial : public ListAsLinkedList{public:    void Differentiate ();};class DifferentiatingVisitor : public Visitor{public:    void Visit (Object& object)    {	Term& term = dynamic_cast<Term&> (object);	term.Differentiate ();    }};void Polynomial::Differentiate (){    DifferentiatingVisitor visitor;    Accept (visitor);    Object& zeroTerm = Find (Term (0, 0));    if (!zeroTerm.IsNull ())    {	Withdraw (zeroTerm);	delete &zeroTerm;    }}