async和await异步操作

class Program
{
static void Main(string[] args)
{
// 同步方式
Console.WriteLine("异步方式测试开始！");
AstbcMethod(35);
Console.WriteLine("异步方式结束！");
Console.ReadKey();
}

private static async void AstbcMethod(int input)
{
Console.WriteLine("进入异步操作！");
var result = await AsyncWork(input);
Console.WriteLine("最终结果{0}", result);
Console.WriteLine("退出异步操作！");
}

private static async Task<int> AsyncWork(int val)
{
for (int i = val; i < 40; i++)
{
Console.WriteLine("耗时操作{0}", i);
var result = await Task.Factory.StartNew((Func<object, int>)Fn, i);
Console.WriteLine("耗时操作j结果{0}", result);
val++;
}
return val;
}

//斐波那契数列
private static int Fn(object n)
{
var i = (int) n;
if (i <= 0)
{
throw new ArgumentOutOfRangeException();
}
if (i == 1 || i == 2)
{
return 1;
}
return checked(Fn(i - 1) + Fn(i - 2)); // when n>46 memory will  overflow
}
}