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Check Credit Card Number

Posted by BrewGuru99 BrewGuru99 on January 30th, 2004
' ' Usage: Returns Boolean indicating whether or not credit card ' number given passes the Luhn Formula (as described in ' ISO/IEC 7812-1:1993). Only numbers and numerical strings ' accepted, remove any spaces and dashes in strings. ' Example: ' booAcceptCard = CheckCC("4000000000000002") ' Function CheckCC(CCNo) Dim I, w, x, y ' y = 0 CCNo = CStr(CCNo) ' 'Process digits from right to left, drop last digit if total 'length is even ' w = 2 * (len(CCNo) Mod 2) ' for I = len(CCNo) - 1 to 1 step -1 x = mid(CCNo, I, 1) ' If IsNumeric(x) then Select Case (I Mod 2) + w Case 0, 3 ' 'Even Digit - Odd where total length is odd '(eg. Visa vs. Amx) ' y = y + CInt(x) Case 1, 2 ' 'Odd Digit - Even where total length is odd ' (eg. Visa vs. Amx) ' x = CInt(x) * 2 If x > 9 then ' 'Break the digits (eg. 19 becomes 1 + 9) ' y = y + (x \ 10) + (x - 10) else y = y + x End If End Select End If next ' 'Return the 10's complement of the total y = 10 - (y Mod 10) ' If y > 9 then y = 0 CheckCC = (CStr(y) = Right$(CCNo, 1)) End Function

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