using System;

public class Person

{

    public int Age {get;set;}

    public static void SetAge(Person person, int age) {

        person = new Person();

        person.Age = age;

    }

    public static void SetAge(ref Person person, int age) {

        person = new Person();

        person.Age = age;

    }

    public static void SetAge(int age, out Person person) {

        person = new Person();

        person.Age = age;

    }

}

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        // Obj

        Person p = new Person();

        p.Age = 18;

        Person.SetAge(p, 20);

        Console.WriteLine(p.Age);

        // By ref

        p = new Person();

        p.Age = 18;

        Person.SetAge(ref p, 20);

        Console.WriteLine(p.Age);

        // By out

        p = new Person();

        p.Age = 18;

        Person.SetAge(20, out p);

        Console.WriteLine(p.Age);

        // NULL Obj

        Person p1 = null;

        Person.SetAge(p1, 20);

        Console.WriteLine(p1);

        // NULL by ref

        Person p2 = null;

        Person.SetAge(ref p2, 20);

        Console.WriteLine(p2);

        // NULL by out

        Person p3;

        Person.SetAge(20, out p3);

        Console.WriteLine(p3);

        Console.WriteLine(p3.Age);

    }

}