using System;

namespace Simple_Caesar_Cypher_in_C_Sharp
{
    class Program
    {
        static Char[] alphabet = new Char[] {'a','b','c','d','e','f','g','h','i',
        'j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','1',
        '2','3','4','5','6','7','8','9','0',' '};

        static String cEncrypt(String toEncrypt, int key)
        {
            String encrypted = "";

            for (int i = 0; i < toEncrypt.Length; i++)
            {
                for (int t = 0; t < alphabet.Length; t++)
                {
                    if (Char.ToLower(toEncrypt[i]) == alphabet[t])
                    {
                        try
                        {
                            encrypted += alphabet[t - key];
                        }
                        catch
                        {
                            encrypted += alphabet[alphabet.Length - (key - t)];
                        }

                        break;
                    }
                }
            }
            return encrypted;
        }

        static String cDecrypt(String toDecrypt, int key)
        {
            String decrypted = "";

            for (int i = 0; i < toDecrypt.Length; i++)
            {
                for (int t = 0; t < alphabet.Length; t++)
                {
                    if (Char.ToLower(toDecrypt[i]) == alphabet[t])
                    {
                        try
                        {
                            decrypted += alphabet[t + key];
                        }
                        catch
                        {
                            decrypted += alphabet[key - (alphabet.Length - t)];
                        }

                        break;
                    }
                }
            }
            return decrypted;
        }

        static void Main(string[] args)
        {
            String answer = "";

            while (true)
            {
                System.Console.Write("Encrypt or Decrypt (E/D): ");
                answer = Console.ReadLine();

                if (answer.ToLower() == "e")
                {
                    int userKey;
                    String userMsg;

                    Console.Write("Message: ");
                    userMsg = Console.ReadLine();
                    while (true)
                    {
                        Console.Write("Key: ");
                        userKey = Convert.ToInt32(Console.ReadLine());

                        if (userKey > 0 && userKey < alphabet.Length)
                        {
                            break;
                        }
                        else
                        {
                            System.Console.WriteLine("Error 01: Key out of range...\n");
                        }
                    }
                    System.Console.WriteLine("\nEncrypted Message: (" + cEncrypt(userMsg, userKey) + ")");
                }
                else if (answer.ToLower() == "d")
                {
                    int userKey;
                    String userMsg;

                    Console.Write("Message: ");
                    userMsg = Console.ReadLine();
                    while (true)
                    {
                        Console.Write("Key: ");
                        userKey = Convert.ToInt32(Console.ReadLine());

                        if (userKey > 0 && userKey < alphabet.Length)
                        {
                            break;
                        }
                        else
                        {
                            System.Console.WriteLine("Error 01: Key out of range...\n");
                        }
                    }
                    System.Console.WriteLine("\nDecrypted Message: (" + cDecrypt(userMsg, userKey) + ")");
                }
                else
                {
                    System.Console.WriteLine("Error 02: Enter E or D...\n");
                }
            }
        }
    }
}