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I'm trying to make a program that encrypts a string the user submits. I want to use an encryption technique where the string is advanced 3 letters in the alphabet.

Example: abc would become def.

Currently I have a TextBox (TextBox1) and a Button (Button1).

My code so far:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
 Dim rawText As String
 rawText = TextBox1.Text
 Dim letterTxt As String = Chr(Asc(rawText) + 3)
 MsgBox(letterTxt)

End Sub

The problem is that when I run it, it only outputs 1 letter.

What did I do wrong?

A Caesar cipher method. Accepts positive and negative shifts and, optionally, a number of alphabet letters.

The latter, to be tested with ASCII tables different than the usual US-ASCII.

It doesn't alter digits (skipped) but you can modify it using the same pattern, if needed.

Use the Scramble parameter to select scramble (True) or unscramble (False).

Sample test code:

Dim Scrambled1 As String = CaesarCipher("ABCXYZabcxyz", 3, True)
Dim Scrambled2 As String = CaesarCipher("ABCXYZabcxyz", -5, True)

'Scrambled1 is now DEFABCdefabc
'Scrambled2 is now VWXSTUvwxstu

Dim Unscrambled As String = CaesarCipher(Scrambled2, -5, false)

'Unscrambled is now ABCXYZabcxyz

Function CaesarCipher(Input As String, CaesarShift As Integer, Scramble As Boolean, Optional AlphabetLetters As Integer = 26) As String

 Dim CharValue As Integer
 Dim MinValue As Integer = AscW("A"c)
 Dim MaxValue As Integer = AscW("Z"c)
 Dim ScrambleMode As Integer = If((Scramble), 1, -1)
 Dim output As StringBuilder = New StringBuilder(Input.Length)

 If Math.Abs(CaesarShift) >= AlphabetLetters Then
 CaesarShift = (AlphabetLetters * Math.Sign(CaesarShift)) - Math.Sign(CaesarShift)
 End If

 For Each c As Char In Input
 CharValue = AscW(c)
 If Not Char.IsNumber(c) Then
 CharValue = CharValue + (CaesarShift * ScrambleMode) Mod AlphabetLetters
 CharValue = If(AscW(Char.ToUpper(c)) + (CaesarShift * ScrambleMode) > MaxValue, CharValue - AlphabetLetters, CharValue)
 CharValue = If(AscW(Char.ToUpper(c)) + (CaesarShift * ScrambleMode) < MinValue, CharValue + AlphabetLetters, CharValue)
 End If
 output.Append(ChrW(CharValue))
 Next
 Return output.ToString()
End Function