Module Module1

    Sub Main()
        Dim GTIN As String

        Dim total As Integer = 0
        Console.WriteLine("please enter a barcode")
        GTIN = Console.ReadLine()


        For i = 1 To 7

            If i Mod 2 <> 0 Then
                total = total + (Mid(GTIN, i, 1) * 3)
            Else
                total = total + (Mid(GTIN, i, 1))
            End If
        Next


        Console.WriteLine("the check digit is" & 10 - (total Mod 10))
        Console.ReadLine()

        Console.WriteLine(GTIN)
        Console.ReadLine()


    End Sub

End Module