向string,int,类对象等中扩展方法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "sss";
            s.Res();
            /**************************/
            student stu = new student("11013141","二货");
            stu.Say();
            stu.sayhello();
        }
    }
    /// <summary>
    /// 扩展方法写在一个静态类中
    /// </summary>
    public static class Test
    {
        public static void Res(this string s)
        {
            Console.WriteLine(s);
        }
        public static void sayhello(this student s)
        {
            Console.WriteLine(" 编号：" + s.No+";姓名：" + s.Name);
        }
    }
    public class student
    {
        //public student() { }
        public student(string no,string name)
        {
            this.No = no;
            this.Name = name;
        }
        private string no;

        public string No
        {
            get { return no; }
            set { no = value; }
        }
        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }
        public void Say()
        {
            Console.WriteLine("姓名："+Name+"; 编号："+No);
        }
    }
}