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

namespace Decrypter
{
    class Program
    {
        static void Main(string[] args)
        {
            String input = "-1";
            while (input != "0")
            {
                Console.WriteLine("Wat wil je doen?");
                Console.WriteLine("1: Iets Caesar decoderen");
                Console.WriteLine("0: Sluiten");
                input = Console.ReadLine();
                switch (input)
                {
                    case "1":
                        CaesarMenu();
                        break;
                    case "0":
                        Console.WriteLine("We sluiten...");
                        break;
                    default:
                        Console.WriteLine("Ken ik niet...");
                        break;
                }
            }

        }
        static void CaesarMenu()
        {
            String input = "-1";
            while (input != "0")
            {
                Console.WriteLine("Geef de Caesar code in ofwel een 0 om te stoppen");
                input = Console.ReadLine();
                if (input != "0")
                {
                    Console.WriteLine("Geef nu de C in");
                    int C = 17;
                    Console.WriteLine("De output is= " + DecypherCaesar(input, C));
                }
            }
        }
        static String DecypherCaesar(String input, int C)
        {
            int strLen = input.Length;
            String output="";
            for (int i = 1; i <= strLen; i++)
            {
                int asc = Convert.ToInt32(Convert.ToSByte(input[i - 1]));
                if(asc >= 65 && asc <= 90){
                    asc = asc - C;
                    if(asc < 65){
                        if (asc == 64)
                            asc = 32;
                        else
                            asc = asc + 27;
                    }
                }

                output+=char.ConvertFromUtf32(asc);
            }
            return output;
        }
    }
}