Hi Enrique,

As Mike had pointed out, you could use ArrayLists or custom collections. You already provided a solution using arrays, which is perfectly valid as well. If you are using .NET 2.0 or superior, another alternative would be to employ generic lists, such as this:

public class A
{
    IList<B> _listOfB = new List<B>();

    public IList<B> ListOfB 
    {
        get { return _listOfB;  }
        set { _listOfB = value; }
    }
}

public class B {}

To use the agregation you might do the following from the user class:

A classA = new A();
classA.ListOfB.Add(new B());
classA.ListOfB.Add(new B());
classA.ListOfB.Add(new B());
classA.ListOfB.Add(new B());

Best regards,