Credit card numbers are not random. In addition to bank and account number there are extra digits. a customer or a clerk hasn't made a mistake typing in the long 16 digit number. In fact even magnetic strip fail, and errors in transmission from a chip reading devices can also fail to send the correct number.

They use something called Luhn' Algorithm to detect errors.

For this lab, we will write and test the validity of a 16 digit credit card.

The practice of extreme programming starts with writing the code to test if Here is a video that explains how it works