An C# implementation of the Luhn algorithm.

The Luhn algorithm is a checksum formula used to validate identification numbers like credit card numbers. It works by doubling every second digit from the right, summing all the digits, and checking if the total is a multiple of 10. It's widely used and is specified in ISO/IEC 7812-1.

Status	Solution	Project Format	.NET Version
	LuhnDotNet.sln	SDK	Standard 2.0
			Standard 2.1
			FX 4.6.2
			FX 4.7
			FX 4.7.1
			FX 4.7.2
			FX 4.8
			.NET 6
			.NET 7
			.NET 8

Build And Test Status	NuGet Version	Git Tag	Target Frameworks
			.NET 6
			.NET 7
			.NET 8
			Standard 2.0
			Standard 2.1
			FX 4.6.2
			FX 4.7
			FX 4.7.1
			FX 4.7.2
			FX 4.8

1. Open a console and switch to the directory, containing your project file.

2. Use the following command to install version 1.1.0 of the LuhnDotNet package:

   dotnet add package LuhnDotNet -v 1.1.0 -f <FRAMEWORK>
   

3. After the completion of the command, look at the project file to make sure that the package is successfully installed.

   You can open the .csproj file to see the added package reference:

   <ItemGroup>
     <PackageReference Include="LuhnDotNet" Version="1.1.0" />
   </ItemGroup>

1. Open a console and switch to the directory, containing your project file.

2. Use the following command to remove the LuhnDotNet package:

   dotnet remove package LuhnDotNet
   

3. After the completion of the command, look at the project file to make sure that the package is successfuly removed.

   You can open the .csproj file to check the deleted package reference.

using System;
using System.Collections.Generic;
using LuhnDotNet;

namespace Example1
{
  public class Program
  {
    public static void Main(string[] args)
    {
      var checkDigit = Luhn.ComputeLuhnCheckDigit("37828224631000");
      //// Must be 5
      Console.WriteLine(checkDigit);
    }
  }
}

using System;
using System.Collections.Generic;
using LuhnDotNet;

namespace Example2
{
  public class Program
  {
    public static void Main(string[] args)
    {
      var luhnNumber = Luhn.ComputeLuhnNumber("37828224631000");
      //// Must be 378282246310005
      Console.WriteLine(luhnNumber);
    }
  }
}

using System;
using System.Collections.Generic;
using LuhnDotNet;

namespace Example3
{
  public class Program
  {
    public static void Main(string[] args)
    {
      var isValid = Luhn.IsValid("378282246310005");
      //// Must be 'true'
      Console.WriteLine(isValid);
    }
  }
}

using System;
using System.Collections.Generic;
using LuhnDotNet;

namespace Example4
{
  public class Program
  {
    public static void Main(string[] args)
    {
      var isValid = Luhn.IsValid("37828224631000", 5);
      //// Must be 'true'
      Console.WriteLine(isValid);
    }
  }
}

The LuhnDotNet library can be used in combination with the ConvertAlphaNumericToNumeric method to validate an International Securities Identification Number (ISIN). An ISIN uniquely identifies a security, such as stocks, bonds or derivatives. It is a 12-character alphanumeric code.

The ConvertAlphaNumericToNumeric method is used to convert the alphanumeric ISIN to a numeric string, where each letter in the input string is replaced by its decimal ASCII value minus 55. This numeric string can then be validated using the Luhn.IsValid method.

Here is an example of how to use these methods to validate an ISIN:

using System;
using LuhnDotNet;

namespace Example5
{
  public class Program
  {
    public static void Main(string[] args)
    {
      string isin = "US0378331005";
      bool isValid = Luhn.IsValid(isin.ConvertAlphaNumericToNumeric());

      Console.WriteLine($"The ISIN {isin} is valid: {isValid}");
    }
  }
}

The LuhnDotNet library provides the ComputeLuhnCheckDigit method which can be used to compute the check digit of a numeric string according to the Luhn algorithm. When dealing with an International Securities Identification Number (ISIN), which is a 12-character alphanumeric code, we first need to convert the alphanumeric ISIN to a numeric string. This can be achieved using the ConvertAlphaNumericToNumeric method.

Here is an example of how to compute the check digit of an ISIN:

using System;
using LuhnDotNet;

namespace Example6
{
  public class Program
  {
    public static void Main(string[] args)
    {
      string isinWithoutCheckDigit = "US037833100";
      byte checkDigit = Luhn.ComputeLuhnCheckDigit(isinWithoutCheckDigit.ConvertAlphaNumericToNumeric());

      Console.WriteLine($"The check digit for ISIN {isinWithoutCheckDigit} is: {checkDigit}");
    }
  }
}

The LuhnDotNet library can be used to compute the check digit of a credit card number. The check digit is the last digit of the credit card number, which is used to validate the number according to the Luhn algorithm.

using System;
using LuhnDotNet;

namespace Example7
{
  public class Program
  {
    public static void Main(string[] args)
    {
      string creditCardNumberWithoutCheckDigit = "4417 1234 5678 911".Replace(" ", "");
      byte checkDigit = Luhn.ComputeLuhnCheckDigit(creditCardNumberWithoutCheckDigit);

      Console.WriteLine($"The check digit for credit card number {creditCardNumberWithoutCheckDigit} is: {checkDigit}");
    }
  }
}

The LuhnDotNet library can be used to validate a credit card number according to the Luhn algorithm. The IsValid method returns true if the credit card number is valid, and false otherwise.

using System;
using LuhnDotNet;

namespace Example8
{
  public class Program
  {
    public static void Main(string[] args)
    {
      string creditCardNumber = "4417 1234 5678 9113".Replace(" ", "");
      bool isValid = Luhn.IsValid(creditCardNumber);

      Console.WriteLine($"The credit card number {creditCardNumber} is valid: {isValid}");
    }
  }
}

For the following instructions, please make sure that you are connected to the internet. If necessary, NuGet will try to restore the xUnit packages.

Use one of the following solutions with dotnet to build LuhnDotNet:

• LuhnDotNet.sln (all, see table)

The syntax is:

dotnet {restore|build|test} -c {Debug|Release} LuhnDotNet.sln

dotnet restore LuhnDotNet.sln

The instructions below are examples, which operate on the LuhnDotNet.sln.

dotnet build -c Debug --no-restore LuhnDotNet.sln

dotnet build -c Release --no-restore LuhnDotNet.sln

dotnet test -c Debug --no-restore --no-build LuhnDotNet.sln

dotnet test -c Release --no-restore --no-build LuhnDotNet.sln