自写扩展方法

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

namespace CsTest
{
static class kuozhan
{
public static string se(this string d)
{
return d.Remove(0,2);
}
public static string  isou(this int ds)
{
if (ds%2==0)
{
return "是个偶数";
}
else
{
return "不是偶数";
}
}
}
}

class Program
{
static void Main(string[] args)
{
string str = "Hello World！";
str.se();
int b = 67;
b.isou();

}
}