Excel UDF - Check the validity of credit card numbers

How to check the validity of credit card numbers or identity card numbers of several countries including Israel and South Africa.
The validity is checked using the Luhn algorithm. This algorithm was designed to protect against accidental mistyping errors and it works like this:
The individual digits are multiplied by 1 or 2 starting from the most right digit (which is the check digit) with 1, the next digit to the left with 2, doing this intermittently with all the numbers. If the result of the multiplication has two digits then these are added one to the other.
The resulting numbers are added to each other including the check digit, and the total sum should be divisible by 10 without a remainder.
In this video I'll show you how to build a User Defined Function in Excel that checks the validity of credit card numbers.
Here’s a link from where you can download an Excel file containing the yk_cCardCheck function: docs.google.co...
Here’s a link from where you can download a pdf file only containing the functions code: drive.google.c...
Here is a link to another video of mine that explains how and where to save User Defined Functions to make them available for all your Excel workbooks: • Excel User Defined Fun... this video is Hebrew spoken but has English subtitles.