Program

The nice thing about this Program class is that it's automated. It scans your executable (assembly) for subclasses of Application, and dynamically creates a selected subclass of Application.

This magic is done trough reflection, using the built-in Assembly.GetTypes method. Because this class will never be edited, i'm just going to give you the code listing. If you are interested in how it works, ask me or do some google-ing on any code you don't recognize.

You select the subclass of Application based on class name of the subclasses!

The code

The one thing we do here that we haven't done before is that the Program class is not in a specific namespace! This is not an error. C# has an anonymous global namespace. If you fail to specify a namespace for a class, it gets put into this global namespace.

Both Program and Application live in the global namespace.

using System.Linq;

// Lives in global namespace
class Program {
    static void Main(string[] args) {
        System.Type[] samples = FindAndPrintApplicationChildClasses();
        System.Type selectedSampleType = null;

        if (samples == null || samples.Length == 0) {
            System.Console.WriteLine("No samples found, press any key to quit");
            System.Console.ReadKey();
            return;
        }

        if (args.Length > 0) {
            selectedSampleType = ParseSampleFromNumber(samples, args[0]);
        }

        System.Console.WriteLine("Select a sample, or q to quit");
        while (selectedSampleType == null) {
            System.Console.Write("Enter a sample number: ", System.ConsoleColor.White);
            string input = System.Console.ReadLine();
            if (!string.IsNullOrEmpty(input) && input.ToLower()[0] == 'q') {
                return;
            }
            selectedSampleType = ParseSampleFromNumber(samples, input);
        }

        Application game = (Application)System.Activator.CreateInstance(selectedSampleType);
        game.Main(args);
    }

    static System.Type[] FindAndPrintApplicationChildClasses() {
        System.Type[] samples = typeof(Application).Assembly.GetTypes().Where(t => t.IsSubclassOf(typeof(Application)) && t != typeof(Application)).ToArray();
        int blockSize = samples.Length / 2;
        for (int i = 0; i < blockSize; i++) {
            System.Console.WriteLine(string.Format("{2,2}. {0,-30}{3,2}. {1,-30}", samples[i].Name, samples[i + blockSize].Name, i, i + blockSize), System.ConsoleColor.DarkGray);

        }
        if (blockSize * 2 < samples.Length) {
            System.Console.WriteLine($"{samples.Length - 1,36}. {samples[samples.Length - 1].Name}", System.ConsoleColor.DarkGray);
        }
        if (samples.Length != 0) {
            System.Console.WriteLine();
        }

        return samples;
    }

    static System.Type ParseSampleFromNumber(System.Type[] samples, string input) {
        int number;
        if (!int.TryParse(input, out number)) {
            System.Console.WriteLine("Invalid format.", System.ConsoleColor.Red);
            return null;
        }

        if (number >= samples.Length || number < 0) {
            System.Console.WriteLine("Invalid number.", System.ConsoleColor.Red);
            return null;
        }

        return samples[number];
    }
}