////   This file contains the C++ code from Program 6.12 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_12.cpp//void RPNCalculator (Stack& stack){    char c;    while (cin >> c, !cin.eof ())    {	if (std::isdigit (c))	    stack.Push (*new Int (c - '0'));	else if (c == '+')	{	    Int& arg2 = dynamic_cast<Int&> (stack.Pop ());	    Int& arg1 = dynamic_cast<Int&> (stack.Pop ());	    stack.Push (*new Int (arg1 + arg2));	    delete &arg1;	    delete &arg2;	}	else if (c == '*')	{	    Int& arg2 = dynamic_cast<Int&> (stack.Pop ());	    Int& arg1 = dynamic_cast<Int&> (stack.Pop ());	    stack.Push (*new Int (arg1 * arg2));	    delete &arg1;	    delete &arg2;	}	else if (c == '=')	{	    Int& arg = dynamic_cast<Int&> (stack.Pop ());	    cout << arg << endl;	    delete &arg;	}    }}