From: James Edward Gray II <james@...>
Date: 2007-04-28T03:20:03+09:00
Subject: Re: [QUIZ] Checking Credit Cards (#122)

On Apr 27, 2007, at 12:58 PM, Matthew Moss wrote:

>>         +============+=============+===============+
>>         | Card Type  | Begins With | Number Length |
>>         +============+=============+===============+
>>         | AMEX       | 34 or 37    | 15            |
>>         +------------+-------------+---------------+
>>         | Discover   | 6011        | 16            |
>>         +------------+-------------+---------------+
>>         | MasterCard | 51-55       | 16            |
>>         +------------+-------------+---------------+
>>         | Visa       | 4           | 13 or 16      |
>>         +------------+-------------+---------------+
>
> So is a card number like "4012 3456 7890" a valid Unknown, or an  
> invalid Visa?

Visa Invalid

Always match the type first.

> Similarly, for Unknown, should we accept any length, or go for the  
> common 16?

Unknown is for any type that doesn't match, so it could be any length.

James Edward Gray II