Problem Statement

The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits. Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:

For example, if the trial number is 49927398716:

Write a function/method/procedure/subroutine that will validate a number with the Luhn test, and use it to validate the following numbers:

Let's start with the solution:

LUHN(C)
 NEW ODD,EVEN,S
 SET S=$REVERSE(C)
 SET ODD=0 FOR I=1:2:$LENGTH(S) SET ODD=ODD+$EXTRACT(S,I)
 SET EVEN=0 FOR I=2:2:$LENGTH(S) SET T=$EXTRACT(S,I)*2 SET EVEN=EVEN+$SELECT(T<=9:T,T>9:$EXTRACT(T,1)+$EXTRACT(T,2))
 QUIT '((ODD+EVEN)#10)