Check if credit card number is valid ?

[nobitavn94]

Hi all ,In .NET 2003 ,I use RegularExpressionValidator control to check if a credit card number is valid by using Luhn algorithm .But I don't know to use what expression ...Help me !Thanks a lot !

[aspnetguy]

try somehtign like this

System.String creditCard = (System.String) values[0];// strip out non-numeric charactersSystem.Text.RegularExpressions.Regex re = new System.Text.RegularExpressions.Regex("[^0-9]");System.String numbers = re.Replace(creditCard, "");// Return the credit card number with only the digits in the stringresult = numbers;// The algorithm to validate a credit card is this// 1) Start from the right, and remove every second digit// 2) Double each of these values// 3) Add each digit in each doubled value together (12 becomes 3, for example)// 4) Add these values back to the remaining digits in the credit card number// 5) Verify that the result is a multiple of 10int total = 0;for (int i = numbers.Length - 2; i >= 0; i -= 2){int num = System.Convert.ToInt32(numbers[i] + "");// double itnum *= 2;// add the digitswhile (num >= 10){total += (num % 10);num = num / 10;}// add to totaltotal += num;}// now add on the unused digitsfor (int i = numbers.Length - 1; i >= 0; i -= 2){total += System.Convert.ToInt32(numbers[i] + "");}if ((total % 10) != 0){throw new System.Exception("Credit card number " + creditCard + " is not valid. The checksum is incorrect.");}

[jesh]

Here's a link to an article that might further explain aspnetguy's method:http://www.codeproject.com/aspnet/creditcardvalidator.asp

[nobitavn94]

Thanks all of you !