AsyncAwait

using System;
using System.Threading.Tasks;

namespace ConsoleApp105
{
    class Program
    {
        static async Task Main()
        {
            await FooAsync();
            await AnotherFooAsync();
        }

        private static async Task FooAsync()
        {
            var num = Foo2Async();

            for (int i = 0; i < 20; i++)
            {
                Console.WriteLine($"FooAsync loop --- {i}");
            }

            Console.WriteLine($"The number returned from Foo2Async is: {await num}");
            Console.WriteLine("Now FooAsync returns.");
        }

        private static async Task<int> Foo2Async()
        {
            var num = new Random().Next(100);
            for (int i = 0; i < 100; i++)
            {
                Console.WriteLine($" Foo2Async loop ------ {i} --- {num}");
                num += i;
            }
            Console.WriteLine("Now Foo2Async returns.");
            return await Task.FromResult(num);
        }

        private static async Task AnotherFooAsync()
        {
            int current = 1;
            int previous = 1;

            Console.WriteLine($"1 -- {previous}\n2 -- {current}");

            for (int i = 0; i < 10; i++)
            {
                int temp = current;
                current += previous;
                previous = temp;
                Console.WriteLine($"3 -- {current}");
            }

            await Task.FromResult(0);
        }
    }
}