Typically the user program does not validate a credit card. The issuing bank does. This is done by submitting the information through a "gateway" service. You would forward the information to the gateway (your credit card merchant service) and they return to you O.K. or not.

If you're writing software for resellers or merchants to use, you can search the web for credit card gateways. There are many out there. Each service will provide you with the information you'll need to transmit credit card information through them.

Good Luck