//
//   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) 2001--2002 by Bruno R. Preiss, P.Eng.  All rights reserved.
//
//   http://www.brpreiss.com/books/opus6/programs/pgm06_12.txt
//
public class Algorithms
{
    public static void Calculator(
	TextReader reader, TextWriter writer)
    {
	Stack stack = new StackAsLinkedList();
	int i;
	while ((i = reader.Read()) > 0)
	{
	    char c = (char)i;
	    if (Char.IsDigit(c))
		stack.Push((int)c - (int)'0');
	    else if (c == '+')
	    {
		int arg2 = (int)stack.Pop();
		int arg1 = (int)stack.Pop();
		stack.Push (arg1 + arg2);
	    }
	    else if (c == '*')
	    {
		int arg2 = (int)stack.Pop();
		int arg1 = (int)stack.Pop();
		stack.Push (arg1 * arg2);
	    }
	    else if (c == '=')
	    {
		int arg = (int)stack.Pop();
		writer.WriteLine(arg);
	    }
	}
    }
}