using System;

public class Program

{

    public static void Main()

    {

        A a = new A();

        Console.WriteLine(a.value);

        setValue(a,1);

        Console.WriteLine(a.value);

        newSetValue(a,2);

        Console.WriteLine(a.value);

        newRefSetValue(ref a,3);

        Console.WriteLine(a.value);

    }

    public static void setValue(A a,int value)

    {

        a.value = value;

    }

    public static void newSetValue(A a, int value)

    {

        a = new A();

        a.value = value;

    }

    public static void newRefSetValue(ref A a, int value)

    {

        a = new A();

        a.value = value;

    }

}

​

public class A

{ 

    public A()

    {

        value = 0;

    }

    public int value { get; set; }

}