using System;

static class Program {
  Level [] levels = new Level [10];
  levels [0] = new Level1 ();

  foreach (var l in levels) {
    if (l != null) {
      Console.WriteLine(l.Name);
    }
  }
}

abstract class Level {
  public int Number { get; protected set; }
  public String Name { get; protected set; }
}

class Level1 : Level {
  public Level1 () {
    this.Number = 1;
    this.Name = "Level 1";
  }
}