ISBN H/W

Module Module1
    Dim ValidCheck As Boolean
    Dim ISBN As String
    Dim Digit(12) As String
    Dim CheckDig As String
    Dim Total(12) As Integer
    Dim Sum As Integer = 0
    Dim Num As Integer = 1


    Sub Main()
        Console.WriteLine("Please enter a 13 digit ISBN number...")
        ISBN = Console.ReadLine()
        CheckDigit()
        Console.ReadKey()
    End Sub

    Function CheckDigit()

        CheckDig = Digit(12)

        For i = 0 To 12
            Digit(i) = (ISBN(i))
            Console.WriteLine(Digit(i))
        Next

        For i = 0 To 11
            Total(i) = Digit(i) * Num
            Sum = Sum + Total(i)
            If Num = 1 Then
                Num = 3
            Else
                Num = 1
            End If
        Next

        If Sum Mod 10 = CheckDig Then
            ValidCheck = True
        End If

        Console.WriteLine(ValidCheck)
        Return ValidCheck
    End Function

End Module