Programming Forums - ROT Decryptor

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- - ROT Decryptor (http://www.programmingforums.org/showthread.php?t=4806)

I have tried to make a program to decrypt simple ROT decryptions which is where if it's like ROT 4 you move each letter 4 spaces down, so A becomes E, W becomes Z and so on. Here is my code:

    Dim ROTIndex As Integer

    Dim Encrypted As String

    Dim Decrypted() As String = ""



    Sub Main()

        Console.WriteLine("Rotation index: ")

        ROTIndex = Console.ReadLine()

        Console.WriteLine("Encrypted text: ")

        Encrypted = Console.ReadLine()

        For Index As Integer = 0 To Encrypted.Length

            Decrypted = Decrypted & Chr(Asc(Encrypted.Substring(Index, 1) + 13))

        Next

        Console.WriteLine("Decrypted Text: " & Decrypted)

    End Sub

It looks all well and good but when I try to run it I get a bug saying "Invalid cast exception -> cast from string "h" to type 'Double' is not valid" and it says it's occurring on the line that says this:

Decrypted = Decrypted & Chr(Asc(Encrypted.Substring(Index, 1) + 13))

Does anybody know why it may be doing this?

Your adding 13 (byte) to a character which should work as they are actually the same thing but no in VB's universe.

Chr(Asc(Encrypted.Substring(Index, 1)) + 13)

For some reason VB's so Unicodified (Grrr! English IS the only language in the world). This works though:

    Dim ROTIndex As Byte

    Dim Buffer As Char()



    Sub Main()

        Console.Write("Rotation index: ")

        ROTIndex = Console.ReadLine()



        Console.Write("Encrypted text: ")

        Buffer = Console.ReadLine()



        For Index As Integer = Buffer.GetLowerBound(0) To Buffer.GetUpperBound(0)

            Buffer(Index) = Chr(Asc(Buffer(Index)) + ROTIndex)

        Next



        Console.WriteLine("Decrypted Text: " & Buffer)



        Console.ReadLine()

    End Sub