自写扩展方法

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace CsTest
 8 {
 9    static class kuozhan
10     {
11        public static string se(this string d)
12        {
13            return d.Remove(0,2);
14        }
15        public static string  isou(this int ds)
16        {
17            if (ds%2==0)
18            {
19                return "是个偶数";
20            }
21            else
22            {
23                return "不是偶数";
24            }
25        }
26     }
27 }

 1  class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             string str = "Hello World！";
 6             str.se();
 7             int b = 67;
 8             b.isou();
 9 
10         }
11     }