public static void DoWork(int i)
        {
            Console.WriteLine($"Task {i} starting");
            Thread.Sleep(2000);
            Console.WriteLine($"Task {i} finished");
        }
        public static void WaitAll()
        {
            Task[] tasks = new Task[10];
            for(int i=0; i<10; i++)
            {
                int taskNum = i; // makes a local copy of the loop counter so that the correct task number is
                //passed into the lambda expression.
                tasks[i] = Task.Run(() => DoWork(taskNum));
            }
            //Waits for all tasks to complete running
            Task.WaitAll(tasks);
            Console.WriteLine("Finished Processing. Press a key to end");
            Console.ReadKey();
        }