ValidcCard

Function IsValidCreditCardNumber(Value As Variant, Optional ByVal IsRequired As _
Boolean = True) As Boolean
Dim strTemp As String
Dim intCheckSum As Integer
Dim blnDoubleFlag As Boolean
Dim intDigit As Integer
Dim i As Integer

On Error GoTo ErrorHandler

IsValidCreditCardNumber = True
Value = Trim$(Value)

If IsRequired And Len(Value) = 0 Then
IsValidCreditCardNumber = False
End If

' If after stripping out non-numerics, there is nothing left,

' they entered junk

For i = 1 To Len(Value)
If IsNumeric(Mid$(Value, i, 1)) Then strTemp = strTemp & Mid$(Value, i, _
1)
Next
If IsRequired And Len(strTemp) = 0 Then
IsValidCreditCardNumber = False
End If

'Handle different lengths for different credit card types

Select Case Mid$(strTemp, 1, 1)
Case "3" 'Amex
If Len(strTemp) <> 15 Then
IsValidCreditCardNumber = False
Else
Value = Mid$(strTemp, 1, 4) & "-" & Mid$(strTemp, 5, _
6) & "-" & Mid$(strTemp, 11, 5)
End If
Case "4" 'Visa
If Len(strTemp) <> 16 Then
IsValidCreditCardNumber = False
Else
Value = Mid$(strTemp, 1, 4) & "-" & Mid$(strTemp, 5, _
4) & "-" & Mid$(strTemp, 9, 4) & "-" & Mid$(strTemp, 13, 4)
End If
Case "5" 'Mastercard
If Len(strTemp) <> 16 Then
IsValidCreditCardNumber = False
Else
Value = Mid$(strTemp, 1, 4) & "-" & Mid$(strTemp, 5, _
4) & "-" & Mid$(strTemp, 9, 4) & "-" & Mid$(strTemp, 13, 4)
End If
Case Else 'Discover - Dont know rules yet
If Len(strTemp) > 20 Then
IsValidCreditCardNumber = False
End If
End Select

'Now check for Check Sum (Mod 10)

intCheckSum = 0
' Start with 0 intCheckSum

blnDoubleFlag = 0
' Start with a non-doubling

For i = Len(strTemp) To 1 Step -1 ' Working backwards
intDigit = Asc(Mid$(strTemp, i, 1)) ' Isolate character
If intDigit > 47 Then ' Skip if not a intDigit
If intDigit < 58 Then
intDigit = intDigit - 48 ' Remove ASCII bias
If blnDoubleFlag Then
' If in the "double-add" phase

intDigit = intDigit + intDigit ' then double first
If intDigit > 9 Then
intDigit = intDigit - 9 ' Cast nines
End If
End If
blnDoubleFlag = Not blnDoubleFlag ' Flip doubling flag
intCheckSum = intCheckSum + intDigit ' Add to running sum
If intCheckSum > 9 Then ' Cast tens
intCheckSum = intCheckSum - 10 ' (same as MOD 10 but
' faster)

End If
End If
End If
Next

If intCheckSum <> 0 Then ' Must sum to zero
IsValidCreditCardNumber = False
End If

ExitMe:
Exit Function
ErrorHandler:
Err.Raise Err.Number, "IsValidCreditCardNumber", Err.Description

End Function

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Validate a credit card numbers
Returns True if valid, False if invalid

Example:
If IsValidCreditCardNumber(Value:="1234-123456-12345", IsRequired:=True)