AsyncPayground.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace AsyncPlayground
{
    class Program
    {
        static void Main(string[] args)
        {
            var asyncCls = new ASyncClass();

            var tasks = new List<Task>();
            for (int i = 0; i < 10; i++)
            {
               tasks.Add(asyncCls.MainTask(i));
            }
            Task.WhenAll(tasks).Wait();

            var tasks2 = Enumerable.Range(0, 10).Select(asyncCls.MainTask);
            Task.WhenAll(tasks2);

            Console.ReadKey();
        }
    }

    public class ASyncClass
    {
        public async Task MainTask(int i)
        {
            Console.WriteLine("Main Task" + i);
            if (i % 2 == 0)
            {
                Console.WriteLine("Awaiting Subtask one" + i);
                await SubTaskOne(i);
            }
            else
            {
                Console.WriteLine("Awaiting Subtask two" + i);
                await SubTaskTwo(i);
            }
            Console.WriteLine("Main Task completed" + i);
        }

        public async Task SubTaskOne(int i)
        {
            Console.WriteLine("SubTask One"+i);
            await Task.Delay(2000);
            Console.WriteLine("SubTask One complete"+i);
        }

        public async Task SubTaskTwo(int i)
        {
            Console.WriteLine("SubTask Two"+i);
            await Task.Delay(5000);
            Console.WriteLine("SubTask Two complete"+i);
        }
    }
}