我们可以用Stopwatch类获得程序的运行时间，在优化代码时，可以用此方法来查看优化前后程序所耗费的时间

static void Main(string[] args){    Stopwatch sw = new Stopwatch();    long num = 0;    sw.Reset();    sw = Stopwatch.StartNew();    for (int i = 1; i < 100000000; i++) num += 1;    sw.Stop();    TimeSpan el = sw.Elapsed;    Console.WriteLine("花费 {0} ", el);    long ms = sw.ElapsedMilliseconds;    Console.WriteLine("花费 {0} 毫秒", ms);    long tk = sw.ElapsedTicks;    Console.WriteLine("花费 {0} ticks", tk);    Console.ReadKey();}

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