Hello everybody. I'm making project for school and it includes a Vigenere Encipher. There are 3 textboxes. Enter the keyword in Textbox 1, Enter message in Textbox 2, Press button, Output displays in Textbox 3. The following code does the job.

Code:
Public Shared Function VIGEncrypt(ByVal cipherTxt As String, ByVal key As String)

        Dim encryptedText As String = ""
        For i As Integer = 1 To cipherTxt.Length
            Dim temp As Integer = Asc(GetChar(cipherTxt, i)) + Asc(GetChar(key, i Mod key.Length + 1))
            encryptedText += Chr(temp)
        Next
        Return encryptedText

    End Function
But, this code shows the output in ASCII beyond the letter Z such as / * & ^. How can this code be modified to only show characters between a - z & A - Z. If I didn't explain it well enough, please let me know. I also don't know whether the solution is simple, but any help would be greatly appreciated. Thanks in advance!