using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var args = "-v -n 2 r -c3".Split(" ");

        var lib = new libgetopt(args) { Debug = true };

        OptArg arg;

        string opt;

        while ((arg = lib.GetOptions()) != -1)

        {

            switch (arg)

            {

                case 'v':

                    L(":Verbose");

                    break;

                case 'n':

                    opt = arg.Arguments;

                    L($":N = {opt}");

                    break;

                case 'c':

                    opt = arg.Arguments;

                    L($":C = {opt}");

                    break;

            }

        }

    }

    static void L(string s) => Console.WriteLine(s);

}

​

public class libgetopt

{

    string[] args;

    int optIdx = 0;

    OptArg optArg;

    public libgetopt(string[] args)

    {

        this.args = args;

    }

    public bool Debug { get; set; }

    public OptArg GetOptions()

    {

        if (args == null || args.Length == 0 || optIdx >= args.Length)

        {

            L("Null/Empty/EOL");

            return -1;

        }

        string opt = args[optIdx];

        string arg = "";

        if (opt == "--")

        {

            // EOL marker, double dash (--).

            L("EOL");

            return -1;

        }

        else if (opt.StartsWith("-"))

        {

            // Option starting with single dash (-).

            if (opt.Length == 1)

            {

                L("Empty option, skip");

                optIdx++;

                return GetOptions();

            }

            else

            {

                char o = opt[1];

                optArg = new(o);

                L($"Valid option (-{o})");

                // Options?

                if (opt.Length > 2)

                {

                    // Argument without whitespace.

                    arg = opt.Substring(2);

                    optArg.Arguments = arg;

                    L($"Argument w/o whitespace ({arg})");

                }

                else if (args.Length > (optIdx + 1) && !args[optIdx + 1].StartsWith("-"))

                {

                    // Whitespace delimited argument.

                    optIdx++;

                    arg = args[optIdx];

                    optArg.Arguments = arg;

                    L($"Argument w/ whitespace ({arg})");

                }

                optIdx++;

                return optArg;

            }

        }

        else

        {

            // Argument starting without dash.

            // Skip.

            L($"Invalid option ({opt}), skip");

            optIdx++;

            return GetOptions();

        }

    }

    private void L(string s) { if (Debug) Console.WriteLine($"[libgetopt] {s}"); }

}

​

public class OptArg

{

    public int Option { get; private set; }

    public string Arguments { get; set; }

    public OptArg(int option)

    {

        Option = option;

    }

    public static implicit operator OptArg(int option) => new OptArg(option);

    public static implicit operator int(OptArg optArg) => optArg.Option;

}