Hello. I might be wrong, but it looks like a credit card check multiplies
each digit by an alternating series of 1's or 2's. You then Sum the
individual digits. If the Total divides by 10, the number is valid. If
this is correct, here is one idea. If you wanted, you can check for leading
characters that are valid for MasterCard, Visa, etc. I used a string
variable since entering a 16 digit number would have to be done as a string.
My credit card showed "Valid" as a check.
I'm not an expert here, so hopefully some ideas here will help.

Function CC_Check(n As String) As Boolean
'// Dana DeLouis
Dim P As Long 'Pointer
Dim Tot As Long
Dim digit As Long
Dim s As Long

Select Case Len(n)
Case 13 To 16
'Valid Length
'// Make Even Length
If Len(n) Mod 2 = 1 Then n = "0" & n

For P = Len(n) To 1 Step -1
'// = = = = = = = = =
'Option #1
'// = = = = = = = = =
' Get Character
s = Mid$(n, P, 1)
' Multiply by 1 or 2
digit = s * (1 + (P Mod 2))
' Sum the individual digits (ie 12 = 1+2=3)
Tot = Tot + ((digit - 1) Mod 9) + 1

'Option #2 - Combines the 3 lines above...
'// = = = = = = = = =
' Tot = Tot + ((Mid$(n, P, 1) * (1 + (P Mod 2)) - 1) Mod 9) + 1
'// = = = = = = = = =

Next P
CC_Check = (Tot Mod 10) = 0

Case Else
'Invalid
CC_Check = "Invalid Length"
End Select

End Function


--
Dana DeLouis
Win XP & Office 2003


"Bob Phillips" wrote in message
...
Here is a simple function


Function ccCheck(rng) As Boolean
Dim i As Long
Dim tmp

With rng
For i = 1 To Len(.Value) - 1
tmp = tmp + Val(Mid(.Value, i, 1))
Next i
ccCheck = tmp Mod 10 = Val(Right(.Value, 1))
End With

End Function

--

HTH

RP
(remove nothere from the email address if mailing direct)


"Stephanie" wrote in message
...
Does anyone know how to do a MOD-10 credit card number check in Excel
2000?
Is there a way to do it using a macro and Visual Basic?