Can anyone help me?
a) I must write a program that encrypts a meesage using rot13
b) Then i must decrypt the skrambled message using 13 as the key.

My code looks like this now:
Option Explicit
Dim mAlfabet As String


Private Sub cmdDeKrypter_Click()
Dim Melding As String
Dim Tegn As String
Dim teller As Single
Dim foran As String
Dim bak As String
Dim antallTegn As Integer
Dim temp As Integer
Dim res As String

Melding = txtMelding.Text
For teller = 1 To Len(Melding)
bak = Right(Melding, Len(Melding) + teller)
Melding = foran & Tegn & bak
txtOutputKrypter.Text = txtOutputKrypter.Text
txtOutputKrypter.Text = ""
Next teller


MsgBox Melding







End Sub



Private Sub cmdKrypter_Click()
Dim Melding As String
Dim Tegn As String
Dim teller As Single
Dim foran As String
Dim bak As String
Dim antallTegn As Integer
Dim temp As Integer
Dim res As String

Melding = txtMelding.Text
For teller = 1 To Len(Melding)
Tegn = Mid$(Melding, teller, 1)
temp = InStr(1, mAlfabet, Tegn, vbBinaryCompare)
Tegn = Mid$(mAlfabet, temp + 13, 1)
foran = Left(Melding, teller - 1)
bak = Right(Melding, Len(Melding) - teller)
Melding = foran & Tegn & bak
txtOutputKrypter.Text = txtOutputKrypter.Text
txtOutputKrypter.Text = ""

Next teller


MsgBox Melding






End Sub

Private Sub Form_Load()
mAlfabet = "abcdefghijklmnopqrstuvwxyzabcdefghijklmn"






End Sub

Private Sub mnuAvslutt_Click()
End

End Sub

Thank you!