////   This file contains the C++ code from Program 6.7 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/pgm06_07.cpp//class StackAsLinkedList : public Stack{    LinkedList<Object*> list;    class Iter;public:    StackAsLinkedList ();    // ...    friend class Iter;};class StackAsLinkedList::Iter : public Iterator{    StackAsLinkedList const& stack;    ListElement<Object*> const* position;public:    Iter (StackAsLinkedList const&);    // ...};