using System;

public class Program

{

    static private char Encrypt(int x)

    {

        char temp;

        switch (x)

        {

            case 0:

                temp = 'A';

                break;

            case 1:

                temp = 'B';

                break;

            case 2:

                temp = 'C';

                break;

            case 3:

                temp = 'D';

                break;

            case 4:

                temp = 'E';

                break;

            case 5:

                temp = 'F';

                break;

            case 6:

                temp = 'G';

                break;

            case 7:

                temp = 'H';

                break;

            case 8:

                temp = 'I';

                break;

            case 9:

                temp = 'J';

                break;

            case 10:

                temp = 'K';

                break;

            case 11:

                temp = 'L';

                break;

            case 12:

                temp = 'M';

                break;

            case 13:

                temp = 'N';

                break;

            case 14:

                temp = 'O';

                break;

            case 15:

                temp = 'P';

                break;

            case 16:

                temp = 'Q';

                break;

            case 17:

                temp = 'R';

                break;

            case 18:

                temp = 'S';

                break;

            case 19:

                temp = 'T';

                break;

            case 20:

                temp = 'U';

                break;

            case 21:

                temp = 'V';

                break;

            case 22:

                temp = 'W';

                break;

            case 23:

                temp = 'X';

                break;

            case 24:

                temp = 'Y';

                break;

            case 25:

                temp = 'Z';

                break;

            default:

                temp = '*';

                break;

        }

​

        return temp;

    }

​

    public static void Main()

    {

        Console.WriteLine("Press enter to generate a key cipher key.");

        Console.ReadLine();

        Console.Clear();

        Random r = new Random();

        int q = r.Next(1, 26);

        Console.WriteLine("Your key is: " + q);

        Console.WriteLine("Press enter to see your cipher text.");

        Console.ReadLine();

        char[] ciphertext = new char[26];

        for (int i = 0; i < 26; i++)

        {

            int shift = (i + q) % 26;

            ciphertext[i] = Encrypt(shift);

        }

​

        string b = new string (ciphertext);

        Console.WriteLine(ciphertext);

        Console.WriteLine("Press enter to type in text to encrypt.");

        Console.ReadLine();

        Console.Clear();

        Console.WriteLine("Please enter you plain text in all capital letters.");

        string plain = Console.ReadLine().ToUpper();

        char[] temp = plain.ToCharArray();

        string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        char[] alpha = alphabet.ToCharArray();

        for (int i = 0; i < plain.Length; i++)

        { int count = 0;

            for (int j = 0; j < 26; j++)

            { count++;

             if (temp[i] == alpha[j])

                {

                    int shift = (j + q) % 26;

                    temp[i] = Encrypt(shift);

                    break;

                }

                    else if(temp[i] != alpha[j]&& count==25)

                    temp[i] = '*';

            }

        }

        string final = new string(temp);

        Console.WriteLine(final);

    }

}