 March 25, 2019
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# TIP: Validating Credit Card Numbers

```Function CheckCard(CCNumber As String) _
As Boolean
Dim Counter As Integer, TmpInt As Integer
Dim Answer As Integer

Counter = 1
TmpInt = 0

While Counter <= Len(CCNumber)

If IsEven(Len(CCNumber)) Then
TmpInt = Val(Mid\$(CCNumber, Counter, 1))
If Not IsEven(Counter) Then
TmpInt = TmpInt * 2
If TmpInt > 9 Then TmpInt = TmpInt - 9
End If
'Debug.Print Counter, TmpInt, Answer
Counter = Counter + 1
Else
TmpInt = Val(Mid\$(CCNumber, Counter, 1))
If IsEven(Counter) Then
TmpInt = TmpInt * 2
If TmpInt > 9 Then TmpInt = TmpInt - 9
End If
'Debug.Print Counter, TmpInt, Answer
Counter = Counter + 1
End If

Wend

If Answer = 0 Then CheckCard = True
End Function

Private Sub cmdCheck_Click()
Msgbox CheckCard(txtNumber)
End Sub``` Comment and Contribute

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