Console calculator Part 3 : The calculator engine

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ConsoleCalculator
{
    class Program
    {
        static void WriteIntro()
        {
            Console.WriteLine("===============================================================================");
            Console.WriteLine("       ______");
            Console.WriteLine("      /_____/                       MINI CONSOLE CALCULATOR");
            Console.WriteLine("     /*/*/*/");
            Console.WriteLine("    /*/*/*/                         Free software");
            Console.WriteLine("   /*/*/*/                          Danny Marivoet 2008");
            Console.WriteLine("  -------");
            Console.WriteLine("           ");
            Console.WriteLine("  Type ? for help.        ");
            Console.WriteLine("           ");
            Console.WriteLine("===============================================================================");
        }

        static void DisplayHelp()
        {
            Console.WriteLine("===============================================================================");
            Console.WriteLine("Simple console expression calculator in C#");
            Console.WriteLine(" ");
            Console.WriteLine("Based on the Desk Calculator proposed by B. Stroustrup (see p75 of his book)");
            Console.WriteLine("I added the use of functions and commands.I did the symbol tables differently.");
            Console.WriteLine(" ");
            Console.WriteLine("This is by far a complete implementation, but it shows the use of a recursive ");
            Console.WriteLine("descent parser. Follow e.g. the action with your debugger in VS, fascinating!");
            Console.WriteLine("The calculator has 3 commands : '?' shows this help,'LIST' shows a list of the");
            Console.WriteLine("currently available variables and 'END' ends the application.");
            Console.WriteLine("It has one function : SQRT, but feel free to add others.");
            Console.WriteLine("It's easy! Really!");
            Console.WriteLine("The typing of commands and functions is not case sensitive.");
            Console.WriteLine("And I admit error handling could be better, but it's a start.");
            Console.WriteLine("Besides calculations with +,-,* and / ,like 3.56*88 you can do things like:");
            Console.WriteLine("'foo=1.5',after enter, the variable foo is stored with a value of 1.5 ");
            Console.WriteLine("Next you can calculate : '6.1 - sqrt(foo)' which should give 4.87525512860841");
            Console.WriteLine("Enjoy this code. It's free. Use it anyway you see fit.");
            Console.WriteLine("Errors in it are also for free, but if you can find any, please let me know.");
            Console.WriteLine(" ");
            Console.WriteLine("===============================================================================");
        }

        static void Main(string[] args)
        {
            Parser Parse = new Parser();
            WriteIntro();
            while (true)    //loop until the END command is given
            {
                Console.Write("*--->");
                Parse.InitScan();
                Parse.InputLine = Console.ReadLine();
                Parse.curr_tok = Parse.get_token();
                if (Parse.curr_tok == Parser.token_value.END) break;//leave while-loop
                if (Parse.curr_tok == Parser.token_value.LIST)
                {
                    Parse.ListVars(); 
                    continue;   //with loop
                }
                if (Parse.curr_tok == Parser.token_value.HELP)
                {
                    DisplayHelp();
                    continue;   //with loop
                }
                if (Parse.curr_tok == Parser.token_value.PRINT) continue; //with loop
                Console.WriteLine(Parse.expr());    //write result
            }     
        }
    }
}