AsciiSwitch (Simple string encryption) VB.NET

 Function AsciiSwitch(InputString As String, ValueToAdd As Integer) As String
        Dim OutputString As String = String.Empty
        Dim c As Char
        For i = 0 To Len(InputString) - 1
            c = InputString.Substring(i, 1)
            OutputString += Chr(Asc(c) + ValueToAdd)
        Next

        Return OutputString
    End Function

'Calling the function

   'lblDecrypted.Text = AsciiSwitchBack(lblEncrypted.Text, 19)
   'lblDecrypted.Text = AsciiSwitch(lblEncrypted.Text, -19)


'AsciiSwitchMod

 Function AsciiSwitchWithMod(InputString As String, ValueToAdd As Integer, ModValue As Integer) As String
        Dim OutputString As String = String.Empty
        Dim c As Char
        For i = 0 To Len(InputString) - 1
            c = InputString.Substring(i, 1)
            If i Mod 5 = 0 Then
                OutputString += Chr(Asc(c) + ValueToAdd + ModValue)
            Else
                OutputString += Chr(Asc(c) + ValueToAdd)
            End If
        Next

        Return OutputString
    End Function

  ' Calling the function

lblEncrypted.Text = AsciiSwitchWithMod(txtInput.Text, 19, 7)
lblDecrypted.Text = AsciiSwitchWithMod(lblEncrypted.Text, -19, -7)