Task

Validate the check digit of an ISBN-13 code:

   Multiply every other digit by  3.
   Add these numbers and the other digits.
   Take the remainder of this number after division by  10.
   If it is  0,   the ISBN-13 check digit is correct.


Use the following codes for testing:

   978-1734314502       (good)
   978-1734314509         (bad)
   978-1788399081       (good)
   978-1788399083         (bad)


Show output here, on this page



See also

   for details:   13-digit ISBN method of validation.       (installs cookies.)


Module Module1
 
    Function CheckISBN13(code As String) As Boolean
        code = code.Replace("-", "").Replace(" ", "")
        If code.Length <> 13 Then
            Return False
        End If
        Dim sum = 0
        For Each i_d In code.Select(Function(digit, index) (index, digit))
            Dim index = i_d.index
            Dim digit = i_d.digit
            If Char.IsDigit(digit) Then
                sum += (Asc(digit) - Asc("0")) * If(index Mod 2 = 0, 1, 3)
            Else
                Return False
            End If
        Next
        Return sum Mod 10 = 0
    End Function
 
    Sub Main()
        Console.WriteLine(CheckISBN13("978-1734314502"))
        Console.WriteLine(CheckISBN13("978-1734314509"))
        Console.WriteLine(CheckISBN13("978-1788399081"))
        Console.WriteLine(CheckISBN13("978-1788399083"))
    End Sub
 
End Module