using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var enemy = new Enemy();

        var player = new Player();

        ChageVidasByRef(ref enemy.vidas);

        ChageVidas(player.vidas);

        Console.WriteLine(enemy.ToString());

        Console.WriteLine(player.ToString());

    }

    static void ChageVidasByRef (ref int vidas) {

        vidas = 99;

    }

    static void ChageVidas (int vidas) {

        vidas = 99;

    }

    abstract class Char {

        public int vidas;   

        public override string ToString() {

            return string.Format("Tengo {0} vidas", vidas); 

        }

    }

    class Enemy : Char { }

    class Player : Char { }

}