////   This file contains the C++ code from Program 6.19 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/pgm06_19.cpp//Object& QueueAsLinkedList::Head () const{    if (count == 0)	throw domain_error ("queue is empty");    return *list.First ();}void QueueAsLinkedList::Enqueue (Object& object){    list.Append (&object);    ++count;}Object& QueueAsLinkedList::Dequeue (){    if (count == 0)	throw domain_error ("queue is empty");    Object& result = *list.First ();    list.Extract (&result);    --count;    return result;}