double luhn checksum barcode

double_luhn.vb

' Output:
'100000000 -> A10000000086
'100000001 -> A10000000164
'100000002 -> A10000000242
'100000003 -> A10000000320
'100000004 -> A10000000407
'100000005 -> A10000000575

Module VBModule

    Sub Main()
        Dim i As Integer
        For i = 0 To 5 Step 1
            Dim val = 100000000 + i
            Dim newVal = barcode(val)
            Console.WriteLine(Str(val) + " -> " + newVal)
        Next i
    End Sub
    
    Function barcode(value As Integer) As String
        barcode = ("A" & Str(value) & Str(luhnSum(value)) & Str(luhnSum(value + 1))).replace(" ", "")
    End Function
    
    Function luhnSum(InVal As String) As Integer
        Dim sum As Integer
             
        sum = 0
         
        Dim strLen As Integer
        strLen = Len(InVal)
         
        Dim i As Integer
        For i = strLen To 1 Step -1
            Dim digit As Integer
            digit = CInt(Mid(InVal, i, 1))
             
            If ((i Mod 2) = 1) Then
                digit = digit * 2
                 
                If (digit > 9) Then
                    digit = digit - 9
                End If
            End If
            
            sum = sum + digit
        Next i
        sum = sum * 9
         
        luhnSum = sum Mod 10
    End Function
    

End Module