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Checking Credit Card Numbers:

If you are running an E-Commerce site, or even a smaller site for your home business, you may decide to handle credit card transactions on-line. One of the most important parts of this process is to check the Credit Card number that a customer enters, to make sure it is a valid credit card.

All credit cards use an alogithm to create a credit card number for each of their cardholders. This number is unique, but they all most meet certain criteria to be valid. The following ASP code will check to see if the number entered is valid. The function will return TRUE if it is a valid credit card, FALSE if it is not valid.

Function GoodCreditCard(CCNum, ByRef CardType) Dim Valid Dim Accumulator Dim Multiplier Dim Resultant Dim LoopCount ' ' If the Credit Card is valid, the variable "VALID" will be set to the literal "TRUE", ' otherwise it will come back as "FALSE". The variable "CARDTYPE" will be returned ' specifying the credit card type. If the card number is invalid, the value assigned ' "CARDTYPE" will be the literal "INVALID". ' ' --- CARDTYPE = "INVALID" Valid = FALSE ' --- Check for existence of '-' characters in Card Number and strip them --- CCNum = Replace(CCnum,"-","") CCNum = Replace(CCnum," ","") ' --- ' 1. If the Credit Card number is less than 11 digits then there is ' an error in the card number. ' --- If Len(CCNum) > 10 Then ' --- ' 2. If the Credit Card number has 13 or 16 digits and the first ' digit has the value of '4' set <CARD>> to 'VISA' and validate. ' --- If (Len(CCNum) = 13 Or Len(CCNum) = 16) And Left(CCNum,1) = "4" Then CARDTYPE = "VISA" End If ' --- ' 3. If the Credit Card number has 15 digits and the first two ' digits have the value of '34' or '37' set <CARD>> to 'AMEX' and ' validate. ' --- If Len(CCNum) = 15 And (Left(CCNum,2) = "34" Or Left(CCNum,2) = "37") Then CARDTYPE = "AMEX" End If ' --- ' 4. If the Credit Card number has 14 digits and the first two ' digits have the value of '30', '36' or '38' set <CARD>> to ' 'DINER' and validate. ' --- If Len(CCNum) = 14 And _ (Left(CCNum,2) = "30" Or Left(CCNum,2) = "36" Or Left(CCNum,2) = "38") Then CARDTYPE = "DINER" End If ' --- ' 5. If the Credit Card number has 16 digits and the first two ' digits have the value between '50' and '56' then set <CARD>> to ' 'ACCESS' and validate. ' --- If Len(CCNum) = 16 And CInt(Left(CCNum,2)) >= 50 And CInt(Left(CCNum,2)) <= 56 Then CARDTYPE = "MASTER" End If ' --- ' 6. If the Credit Card number has 16 digits and the first two ' digits has the value '35' set <CARD>> to 'JCB' and validate. ' --- If Len(CCNum) = 16 And Left(CCNUM,2) = 35 Then CARDTYPE = "JCB" End If If Len(CCNum) = 16 And CARDTYPE = "INVALID" Then CARDTYPE = "DISCOVER" End If If CARDTYPE <> "INVALID" Then ' --- ' VALIDATE PROCESS: ' ' 7. Start by zeroing an accumulator. ' --- Accumulator = 0 ' --- ' 8. With the Credit Card number, start at the right most digit and ' multiply by 1, then the next prior digit by 2 and continue the ' process of multiplication by 1 and then by 2 until all digits ' have been multiplied. ' --- Multiplier = 1 For LoopCount = Len(CCNum) to 1 Step -1 Resultant = (Mid(CCNum,LoopCount,1) * Multiplier) ' --- ' 9. If the result of a multiplication is less than 10 add to the ' accumulator. ' --- If Resultant < 10 Then Accumulator = Accumulator + Resultant Else ' --- ' 10. If the result of a multiplication is 10 or greater add the two ' digits together and add to the accumulator. ' ' ' Example: 9 x 2 = 18 ' ' Therefore 1 + 8 = 9 ' ' Add 9 to the accumulator. ' --- Accumulator = Accumulator + Left(Resultant,1) + Right(Resultant,1) End If If Multiplier = 1 Then Multiplier = 2 Else Multiplier = 1 End If Next ' --- ' 11. Divide the accumulated value by 10. If no remainder then it is ' a valid card number. If any remainder then it is an invalid ' card number. ' --- If Int(Accumulator/10) * 10 = Accumulator Then Valid = TRUE End If End If If CARDTYPE = "INVALID" Then Valid = FALSE End If End If '''''''''''''''''''''''''''''''' ' Put in 123 for test MC if CCNum = "123" then VALID = TRUE CARDTYPE="TEST" end if GoodCreditCard = VALID end function

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