Luhn Credit Card Validation (code included)

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I’ve been working on this a bit lately and thought I’d share a simplistic routine to verify credit card numbers.
This takes input as a numeric string and tells you if the card should be valid or not - for American Express, Discover, Visa, mastercard, Diner’s Club, Maestro, and anything else out there (any number of digits)
Of course there can still be counterfeit cards, or invalid cvc codes or billing problems, but the payment processor takes care of that. This is simply another short check you can do before sending the number to your server.


Function Luhn(ccnumber As String) As String
	N=[]
	Tot=0
	For x=LEN(ccnumber) To 0 Step -1
		N.Push(ccnumber.mid(X,1).ToInt())
	Next
	For x=1 to LEN(ccnumber) Step 2
		Tot=Tot+N[X]
	Next
	For x=2 to LEN(ccnumber) Step 2
		N[X]=N[X]*2
		If N[X]>9
			Tot=Tot+1+(N[X]-10)
		Else
			Tot=Tot+N[X]
		End If
	Next
	Print "Total: ";Tot
	If (Tot.ToStr()).Right(1)="0"
		Return "VALID CARD"
	Else
		Return "INVALID CARD"
	End If
End Function

It’s short enough for me but I’m sure someone here could make it much more efficient. :slightly_smiling_face: Have fun.