Program.cs

using System;
using System.Threading.Tasks;

namespace asyncAwaitSample
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			var m = new MainClass ();
			var t = m.RunSequential ();
			var t2 = m.RunPararell ();
			var t3 = m.RunSequentialNoAwait ();
			Task.WaitAll (t, t2, t3);
		}

		public async Task RunSequential ()
		{
			Console.WriteLine ("* Run Sequential *");
			var t = await new Scene ("*").Run ();
			var t2 = await new Scene ("*").Run ();
			Console.WriteLine ("* sum: {0} *", t + t2);
		}

		public Task RunSequentialNoAwait ()
		{
			Console.WriteLine ("$ Run Sequential NoAwait $");
			var tt = new Scene ("$").Run ().ContinueWith ((t) => {
				new Scene ("$").Run ().ContinueWith ((t2) => {
					Console.WriteLine ("$ sum: {0} $", t.Result + t2.Result);
				}).Wait ();
			});
			return tt;
		}

		public Task RunPararell ()
		{
			Console.WriteLine ("- Run Pararell -");
			var t = new Scene ("-").Run ();
			var t2 = new Scene ("-").Run ();
			return Task.WhenAll (t, t2).ContinueWith (((Task arg) => 
				Console.WriteLine ("- sum: {0} -", t.Result + t2.Result)));
		}
	}

	class Scene
	{
		private String tag;

		public Scene (String name)
		{
			this.tag = name;
		}

		public void p (String prefix, int v)
		{
			Console.WriteLine ("{3} id={2} {0}: {1} {3}", prefix, v, this.GetHashCode (), tag);
		}

		public async Task<int> Run ()
		{
			p ("start", 0);
			int a = await Task.FromResult (10);
			p ("a", a);

			await Task.Delay (200);

			int b = await Task.FromResult (20);
			p ("b", b);
			return a + b;
		}
	}
}

* Run Sequential *
* id=421107885 start: 0 *
* id=421107885 a: 10 *
- Run Pararell -
- id=301241367 start: 0 -
- id=301241367 a: 10 -
- id=880988194 start: 0 -
- id=880988194 a: 10 -
$ Run Sequential NoAwait $
$ id=924151092 start: 0 $
$ id=924151092 a: 10 $
* id=421107885 b: 20 *
* id=551977066 start: 0 *
* id=551977066 a: 10 *
* id=551977066 b: 20 *
* sum: 60 *
- id=301241367 b: 20 -
- id=880988194 b: 20 -
- sum: 60 -
$ id=924151092 b: 20 $
$ id=277322821 start: 0 $
$ id=277322821 a: 10 $
$ id=277322821 b: 20 $
$ sum: 60 $