测试一个方法的运行时间

using System;
using System.Collections.Generic;
using System.Text;
using System.Diagnostics;

namespace UserPai
{
    class Program
    {
       static decimal pai;
       static decimal loop;
        static void Main(string[] args)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (int i = 1; i < 100000001; i++)
            {
                loop = (decimal)1 / (2 * i-1);

if (i % 2 == 0)
                {
                    loop = -loop;
                }
                pai += loop;
            }
            sw.Stop();
            Console.WriteLine( 4*pai);
            Console.WriteLine(sw.ElapsedMilliseconds);
            Console.ReadLine();
        }
    }
}

Stopwatch