FinalExamPrep-24.07.2019-02.Song

using System;
using System.Text.RegularExpressions;

namespace _02.SongEcryption
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();

            while (input != "end")
            {
                Regex regex = new Regex(@"^([A-z][a-z' ]+):([A-Z ]+)$");
                Match matches = regex.Match(input);

                if (matches.Success)
                {
                    string artist = matches.Groups[1].Value;
                    string song = matches.Groups[2].Value;
                    string newArtist = "";
                    int key = artist.Length;
                    int valueArtist;
                    int valueSong;
                    string newSong = "";

                    for (int i = 0; i < key; i++)
                    {
                        char current = artist[i];
                        if (current != ' ' && current != '\'')
                        {

                            valueArtist = current + key;
                            if (char.IsLower(current) && valueArtist > 'z')
                            {

                                valueArtist = valueArtist - 'z' + ('a' - 1);
                            }
                            if (char.IsUpper(current) && valueArtist > 'Z')
                            {
                                valueArtist = valueArtist - 'Z' + ('A' - 1);
                            }
                            newArtist += (char)valueArtist;
                        }
                        else
                        {
                            newArtist += current;
                        }
                    }
                    for (int i = 0; i < song.Length; i++)
                    {
                        char currentLetter = song[i];
                        if (currentLetter != ' ' && currentLetter != '\'')
                        {
                            valueSong = currentLetter + key;
                            if (char.IsLower(currentLetter) && valueSong > 'z')
                            {
                                valueSong = valueSong - 'z' + ('a' - 1);
                            }
                            if (char.IsUpper(currentLetter) && valueSong > 'Z')
                            {
                                valueSong = valueSong - 'Z' + ('A' - 1);
                            }
                            newSong += (char)valueSong;

                        }
                        else
                        {
                            newSong += currentLetter;
                        }
                    }
                    //string password = newArtist + "@" + song;

                    Console.WriteLine($"Successful encryption: {newArtist}@{newSong}");
                }
                else
                {
                    Console.WriteLine("Invalid input!");
                }
                input = Console.ReadLine();
            }
        }
    }
}