Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'These are my variables'
        Dim i As Integer
        Dim j As Integer

        Dim name As String
        Dim postcode As String
        Dim numberarray(7) As Integer
        Dim check_digit As Integer
        Dim total As Integer
        Dim cardnumber As Integer
        'This assigns the textboxes'
        name = (Txtname.Text)
        postcode = (Txtpostcode.Text)
        cardnumber = (Txtcardnumber.Text)
        'This our first array variable which
        For i = 0 To 7
            numberarray(i) = Txtcardnumber.Text.Substring(i, 1)
        Next
        'this stores the 8th digit as check_digit'
        check_digit = numberarray(7)
        'This reverses the digits'
        Array.Reverse(numberarray)

        For j = 0 To 6
            numberarray(j) = Txtcardnumber.Text.Substring(j, 1)
        Next
        'This multiplies the digits'
        numberarray(0) = numberarray(0) * 2
        numberarray(2) = numberarray(2) * 2
        numberarray(4) = numberarray(4) * 2
        numberarray(6) = numberarray(6) * 2
        'This will take 9 away from the digits if they are greater than 9'
        If numberarray(0) > 9 Then
            numberarray(0) = numberarray(0) - 9
        End If

        If numberarray(2) > 9 Then
            numberarray(2) = numberarray(2) - 9
        End If

        If numberarray(4) > 9 Then
            numberarray(4) = numberarray(4) - 9
        End If

        If numberarray(6) > 9 Then
            numberarray(6) = numberarray(6) - 9
        End If
        'This is all the digits being added up together'
        total = numberarray(0) + numberarray(1) + numberarray(2) + numberarray(3) + numberarray(4) + numberarray(5) + numberarray(6) + check_digit

        MessageBox.Show(total)
        'This checks if the total is directly divisible by 10'
        If total Mod 10 = 0 Then
            'these show the name, postcode, cardnumber and if the cardnumber is valid'
            MessageBox.Show("Name:" & name)
            MessageBox.Show("Postcode:" & postcode)
            MessageBox.Show("cardnumber:" & cardnumber)
            MessageBox.Show("Card is valid")
            MessageBox.Show("Your Loyalty card is Valid")
            'these show the name, postcode, cardnumber and if the cardnumber is invalid'
        ElseIf MessageBox.Show("Name:" & name) Then
            MessageBox.Show("Postcode:" & postcode)
            MessageBox.Show("cardnumber:" & cardnumber)
            MessageBox.Show("Card is invalid")
            MessageBox.Show("Your Loyalty card is Invalid")

        End If
    End Sub
End Class