Curious About Credit Card Validity? Discover How the Luhn Algorithm Works!

I'm not sure how true it is. I didn't verify. You can check it out!

Luhn algorithm - Wikipedia, the free encyclopedia

Luhn algorithm

Now, the question is how can we check whether a given credit card number is valid. The algorithm involved in this checking is called the Luhn algorithm (AKA Sum10 algorithm, AFAIK). Consider a number, say, 5168254236021548. To understand if this is a valid CC#, you should follow 4 easy guidelines:

1. Starting from the leftmost digit, we simply multiply alternating numbers by two. i.e., we multiply the shown bold numbers by two:
5168254236021548
5 * 2 = 10
6 * 2 = 12
2 * 2 = 4
4 * 2 = 8
3 * 2 = 6
0 * 2 = 0
1 * 2 = 2
4 * 2 = 8

2. Add the separate digits of all the products, as follows:
1 + 0 + 1 + 2 + 4 + 8 + 6 + 0 + 2 + 8 = 32

3. Add the unaffected digits to the product, i.e.,
1 + 8 + 5 + 2 + 6 + 2 + 5 + 8 = 37

4. Add the result of steps 2 and 3 and divide it by 10
32 + 37 = 69
69 % 10 = 9

5. If the answer is 0, this is a valid CC#, otherwise, it is not! So, 5168254236021548 is an invalid CC# (since 69 % 10 is 9, not 0).

I don't think it's true... or maybe I am doing the wrong calculation because my credit card is coming up as an invalid number.

Any suggestions?

Credit card numbers are not assigned at random. Each number, usually 16 digits long, must adhere to certain mathematical conditions to be valid. This is called the Luhn Check, and it is used by almost all major cards. If you support a Web site that accepts online payments, the first step in any process that accepts credit card numbers should be verifying the number. This tip shows how you can do this using VB6.
Using VB6, the credit card number is passed, as a string, to the function CCNumberValid. The string must contain only digits—no embedded spaces or dashes. The function returns True if the number is valid and False if not.