daniel and emma watson dating - Validating a credit card

These may include checking the total number of digits, the number prefix, etc.

The table below shows acceptable values for some of the major credit cards.

validating a credit card-74

Here's how the algorithm for the Luhn formula works.

Starting with a given credit card number, 1 2 3 4 - 5 6 7 8 - 9 0 1 2 - 3 4 5 2 we reverse the number, removing any non-numeric characters, to create a new string of digits like this (note that the checksum is now the first digit): 2 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 Now we'll look at each individual digit.

If it is not divisible by 10, the number is invalid." This is NOT true.

Here's how to do it: Step 4 - Add up all the digits in this number (except the checksum) Step 5 - If (sum x 9) MOD 10 = checksum, you have a valid card! If you were to do this in QBASIC, it would look like this: A = 0 FOR X = LEN(CARD$) - 1 TO 1 STEP -2 W = VAL(MID$(CARD$, X,1)) * 2 IF W 1 THEN A = A VAL(MID$(CARD$, X-1, 1)) NEXT X IF (A * 9) MOD 10 = VAL(RIGHT$, CARD$, 1) THEN PRINT "GOOD CARD! " Variables --------- A is the accumulator, adding up the digits on the card, every other one, doubled (doubled -9 if over 9).

When actually processing a transaction, you'd also want to check the customer name, expiration date, etc. The code demonstrated here is really just a first step, meant to help the user by checking for typos or invalid characters.

It can also help you by eliminating processing on the server for card numbers that are obviously not valid.1 0 4 6 2 2 0 1 8 8 1 4 6 1 0 4 6 2 2 = 58 Using the total (58) you'd take the next highest number that is evenly divisible by ten and subtract the total from this to produce the proper checksum digit (60 - 58 = 2 in this case).If the total was already an even multiple of ten, say 70, the checksum would simply be zero.The result should be the last digit on the card (if it's a good number!) Can you please provide an example value (not a valid card number, obviously) where your code and the article's code disagree?Rather than adding up the other digits and calculating the valid checksum value for comparison, it's included in the total to save some programming steps.

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