Create Electronically Sign Credit Card Number with airSlate SignNow

Create electronically sign credit card number

Okay. Now that we've introduced this input validity problem, let's work toward a situation, which is going to lead towards a programming problem for you where you have to solve this kind of problem. The specific problem that we're going to look at is generating valid credit card numbers. And so you might ask the question, "Why would we care about generating valid credit card numbers?" and the assumption here is that you are working on some software under test whose input domain is valid credit card numbers. And so your software under test is probably doing something like processing payments and its output is going to be something like completed transactions. So now how are you going to test this? Well, one thing you're going to do is collect some credit cards that you have and that your friends have. And so you'll have a variety of Mastercard and American Express and other kinds of credit cards. You're going to run it through your payment processing system and you're going to see if it works. After you're finished doing that, the question you have to ask is "Have you shaken all the bugs out of your code?" and the answer is probably not. So what we're going to want to do is randomly generate valid credit card numbers and use that to test the payment processing system. To get any further here, what we're going to have to do is take a look at the structure of a credit card number so here's how those work. So there are some number of digits at the start of a credit card number, so let's say 6, that constitute the issuer identifier. What this means is that for example all of the American Express cards issued by a certain company are going to share an issuer identifier. The next set of digits, let's say 8 of them, is going to correspond to the account number for this credit card and then finally at the end is a check digit. And this is computed algorithmically from the preceding numbers, and the function of the check digit is to serve as a validity check for a credit card number. So if I'm entering my credit card into a website or if I'm swiping my credit card and the magnetic strip has gotten corrupted it's fairly likely that if any of these digits are wrong the check digit is going to catch it and the credit card number can be rejected rapidly and algorithmically other than actually having to submit this thing to somebody who can process the payments and forcing them to reject it when the account number or the issuer identifier fails to look up correctly. The check digit is computed using something called Luhn's algorithm. So this fellow Luhn was a guy who worked for IBM during the middle part of the 20th century. And in 1960, he patented Luhn's algorithm which was simply a method for calculating this check digit and it has been used ever since in applications like this. Let's look at how to use Luhn's algorithm to calculate a check digit. So what we're going to have is a sequence of numbers, and this will work for any number. And now there are two cases. If there's an odd number of digits, we're going to do one thing. And if there's an even number, there'll be a slight variation. If there's an odd number of digits, what we're going to do is go through the digits and take every even-numbered digit and multiply it times 2. So the odd digits we're going to leave alone and the even ones we're going to multiply times 2. And the next thing we're going to have to do is see if any of the resulting numbers are greater than 9. If so, we're going to have to subtract 9 and some number is going to result.