using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleApplication3

{

    class AA

    {

        string s;

        public AA()

        {

            s = "";

        }

        public string S

        {

            get {return s;}

            set { s = value; }

        }

    }

    class Program

    {

        static void change(AA t)

        {

            t.S = "";

        }

        static void Main(string[] args)

        {

            AA t = new AA();

            Console.WriteLine(t.S);

            change(t);

            Console.WriteLine(t.S);

        }

    }

}