Source code in the csharp programming language

    public static class Luhn
    {
        public static bool LuhnCheck(this string cardNumber)
        {
            return LuhnCheck(cardNumber.Select(c => c - '0').ToArray());
        }

        private static bool LuhnCheck(this int[] digits)
        {
            return GetCheckValue(digits) == 0;
        }

        private static int GetCheckValue(int[] digits)
        {
            return digits.Select((d, i) => i % 2 == digits.Length % 2 ? ((2 * d) % 10) + d / 5 : d).Sum() % 10;
        }
    }

    public static class TestProgram
    {
        public static void Main()
        {
            long[] testNumbers = {49927398716, 49927398717, 1234567812345678, 1234567812345670};
            foreach (var testNumber in testNumbers)
                Console.WriteLine("{0} is {1}valid", testNumber, testNumber.ToString().LuhnCheck() ? "" : "not ");
        }
    }


using System;
using System.Linq;

namespace Luhn
{
    class Program
    {
        public static bool luhn(long n)
        {
            long nextdigit, sum = 0;            
            bool alt = false;            
            while (n != 0)
            {                
                nextdigit = n % 10;
                if (alt)
                {
                    nextdigit *= 2;
                    nextdigit -= (nextdigit > 9) ? 9 : 0;
                }
                sum += nextdigit;
                alt = !alt;
                n /= 10;
            }
            return (sum % 10 == 0);
        }

        public static bool luhnLinq(long n)
        {
            string s = n.ToString();
            return s.Select((c, i) => (c - '0') << ((s.Length - i - 1) & 1)).Sum(n => n > 9 ? n - 9 : n) % 10 == 0;
        }

        static void Main(string[] args)
        {            
            long[] given = new long[] {49927398716, 49927398717, 1234567812345678, 1234567812345670};
            foreach (long num in given)
            {
                string valid = (luhn(num)) ? " is valid" : " is not valid";
                Console.WriteLine(num + valid);
            }
            
        }
    }
}


using System;
namespace Luhn_Test
{
	public static class Extensions 
	{
		public static string Reverse(this string s )
		{
		    char[] charArray = s.ToCharArray();
		    Array.Reverse( charArray );
		    return new string( charArray );
		}
	}
	class Program
	{
		public static bool Luhn(long x)
		{
			long s1=0;
			long s2=0;
			bool STATE=x%10!=0; // If it ends with zero, we want the order to be the other way around
			x=long.Parse(x.ToString().Reverse());
			while (x!=0)
			{
				s1+=STATE?x%10:0;
				s2+=STATE?0:((x%10)*2>9)?(((x%10)*2/10)+((x%10)*2)%10):((x%10)*2); 
				STATE=!STATE; //Switch state
				x/=10; //Cut the last digit and continue
			}
			return ((s1+s2)%10==0); //Check if it ends with zero, if so, return true, otherwise,false.
		}
		public static void Main(string[] args)
		{
			long[] ks = {1234567812345670, 49927398717, 1234567812345678 ,1234567812345670 };
			foreach (long k in ks)
			{
			Console.WriteLine("{0} is {1} Valid.",k,Luhn(k)?"":"Not");	
			}
		Start:
			try { 
			Console.WriteLine("Enter your credit:");
			long x=long.Parse(Console.ReadLine());
			Console.WriteLine("{0} Valid.",Luhn(x)?"":"Not");
			goto Start;
			}
			catch (FormatException)
			{
				goto Start;
			}			
		}
	}
}


using System;
using System.Linq;

public class CreditCardLogic
{
    static Func<char, int> charToInt = c => c - '0';

    static Func<int, int> doubleDigit = n => (n * 2).ToString().Select(charToInt).Sum();

    static Func<int, bool> isOddIndex = index => index % 2 == 0;

    public static bool LuhnCheck(string creditCardNumber)
    {
        var checkSum = creditCardNumber
            .Select(charToInt)
            .Reverse()
            .Select((digit, index) => isOddIndex(index) ? digit : doubleDigit(digit))
            .Sum();

        return checkSum % 10 == 0;
    }
}


using System;
using EuropaRTL.Utilities;

public static partial class Algoritmhs
{
    public static bool CheckLuhn(long n)
    {
        int s1 = n.Shatter(true).Subset(2).Arithmetic('+');
        int s2 = n.Shatter(true).Subset(1, -1, 2).ArithmeticRA('*', 2).ShatterAndSum().Arithmetic('+');
        return (s1 + s2) % 10 == 0 ? true : false;
    }
}
class Program
{
    static void Main(string[] args)
    {
        long[] ll = {
                49927398716,
                49927398717,
                1234567812345678,
                1234567812345670
            };
        foreach (var item in ll)
        {
            item.ToString().WriteLine();
            Algoritmhs.CheckLuhn(item).ToString().WriteLine();
        }
        Console.ReadKey();
    }
}