E-Commerce Tip: Programmatically Validate Credit Card Numbers

Before I accept any credit card number into my application, I run a simple numerical validation against it. All major credit cards (American Express, Discover, MasterCard, and Visa) use the Luhn algorithm to validate the numbers—why not you? Although this function doesn't go the extra step of actually running the card to see if the transaction will work, it will give you a simple true/false result regarding the card number's validity. The function also ignores all non-digit characters, so your users can enter the number however they wish.

This is the function to run the algorithm on a given string of numbers:

/// <summary>
/// Validates a credit card number using the standard Luhn/mod10
/// validation algorithm.
/// </summary>
/// <param name="cardNumber">Card number, with or without
///        punctuation</param>
/// <returns>True if card number appears valid, false if not
/// </returns>
public bool IsCreditCardValid(string cardNumber)
{
   const string allowed = "0123456789";
   int i;

   StringBuilder cleanNumber = new StringBuilder();
   for (i = 0; i < cardNumber.Length; i++)
   {
      if (allowed.IndexOf(cardNumber.Substring(i, 1)) >= 0)
         cleanNumber.Append(cardNumber.Substring(i, 1));
   }
   if (cleanNumber.Length < 13 || cleanNumber.Length > 16)
      return false;

   for (i = cleanNumber.Length + 1; i <= 16; i++)
      cleanNumber.Insert(0, "0");

   int multiplier, digit, sum, total = 0;
   string number = cleanNumber.ToString();

   for (i = 1; i <= 16; i++)
   {
      multiplier = 1 + (i % 2);
      digit = int.Parse(number.Substring(i - 1, 1));
      sum = digit * multiplier;
      if (sum > 9)
         sum -= 9;
      total += sum;
   }
   return (total % 10 == 0);
}

About the Author

Eric Smith is the owner of Northstar Computer Systems, a Web-hosting company based in Indianapolis, Indiana. He is also a MCT and MCSD who has been developing with .NET since 2001. In addition, he has written or contributed to 12 books covering .NET, ASP, and Visual Basic.



Comments

  • P!P?P0QP8P1P>!

    Posted by Arel_V on 08/08/2007 04:14am

    P!P?P0QP8P1P> P>P3QP>PP5 P7P0 QQP0QQQ, P>QP5P=Q P?P>P

    P3P;P0.

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • When individual departments procure cloud service for their own use, they usually don't consider the hazardous organization-wide implications. Read this paper to learn best practices for setting up an internal, IT-based cloud brokerage function that service the entire organization. Find out how this approach enables you to retain top-down visibility and control of network security and manage the impact of cloud traffic on your WAN.

  • U.S. companies are desperately trying to recruit and hire skilled software engineers and developers, but there is simply not enough quality talent to go around. Tiempo Development is a nearshore software development company. Our headquarters are in AZ, but we are a pioneer and leader in outsourcing to Mexico, based on our three software development centers there. We have a proven process and we are experts at providing our customers with powerful solutions. We transform ideas into reality.

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date