Private Sub ValidateISBN()
        
	Dim iTotalISBN13 As Integer
        Dim iTotalISBN10 As Integer
        
	Dim iLastDigit13 As Integer
        Dim iLastDigit10 As Integer
        
	Dim sISBN13 As String = "9780375840401"
        Dim sISBN10 As String = "0312349491"

        iTotalISBN10 = 10 * Convert.ToInt32(sISBN10.Substring(0, 1))
        iTotalISBN10 = iTotalISBN10 + 9 * Convert.ToInt32(sISBN10.Substring(1, 1))
        iTotalISBN10 = iTotalISBN10 + 8 * Convert.ToInt32(sISBN10.Substring(2, 1))
        iTotalISBN10 = iTotalISBN10 + 7 * Convert.ToInt32(sISBN10.Substring(3, 1))
        iTotalISBN10 = iTotalISBN10 + 6 * Convert.ToInt32(sISBN10.Substring(4, 1))
        iTotalISBN10 = iTotalISBN10 + 5 * Convert.ToInt32(sISBN10.Substring(5, 1))
        iTotalISBN10 = iTotalISBN10 + 4 * Convert.ToInt32(sISBN10.Substring(6, 1))
        iTotalISBN10 = iTotalISBN10 + 3 * Convert.ToInt32(sISBN10.Substring(7, 1))
        iTotalISBN10 = iTotalISBN10 + 2 * Convert.ToInt32(sISBN10.Substring(8, 1))

        iTotalISBN13 = Convert.ToInt32(sISBN13.Substring(0, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(1, 1)) * 3
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(2, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(3, 1)) * 3
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(4, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(5, 1)) * 3
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(6, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(7, 1)) * 3
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(8, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(9, 1)) * 3
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(10, 1)) * 1
        iTotalISBN13 = iTotalISBN13 + Convert.ToInt32(sISBN13.Substring(11, 1)) * 3
        iLastDigit13 = 10 - (iTotalISBN13 Mod 10)

        If iLastDigit13 = Convert.ToInt32(sISBN13.Substring(12, 1)) Then
            MessageBox.Show("ISBN13 is valid")
        Else
            MessageBox.Show("ISBN13 is not valid")
        End If

        iLastDigit10 = 11 - (iTotalISBN10 Mod 11)

        If iLastDigit10 = Convert.ToInt32(sISBN10.Substring(9, 1)) Then
            MessageBox.Show("ISBN10 is valid")
        Else
            MessageBox.Show("ISBN10 is not valid")
        End If

End Sub