modify deep copy

[BruceWayneLinxu]

I would like to make it deep copy, and the pointer b.a should not be deleted.

[patmorin]

I agree that this makes much more sense from a software engineering perspective. But, the book was originally written in Java and I want to stick with the convention that array assignment is just a constant-time pointer change. In fact, the only reason for the array class in the C++ version is so that an array remembers its length.

[tekinozbek]

I think you can close #65 too then; it's the associated issue for this merge.