Design classes in OOP?

I reviewed some classes of Qt and I feel that they are designed very cool. I need books to learn how to design classes effectly and easily modified codes in the future. Please suggest me some titles. Thanks.

In order to design reusable frameworks I think you need first and foremost experience.
I am not sure how books can help, other that bringing certain design patterns to your knowledge.

If you looked at the Qt classes you must have noticed the predominant use of the PIMPL pattern. There are a few threads about that here, on Qt Centre, so you should read those first.

Thank you. Really, I is a programmer about 2 years, and I also have good knowledge about OOP but almost of programs I wrote are designed by other ones. I want to become a designer, to study how to design classes and avoid mistakes in design. Thanks.

Please suggest me some ebooks about PIMPL pattern. Thanks.

Did you try wikipedia? And any book that has "Design Patterns" in its title?

In this regards, I think books can help you mold your thoughts in a better way

I would recommend that you read the Head First Design Patterns and Head First Object Oriented Analysis and Design. When you skim through these books you may find them childish at first, but this impression will soon change once you start reading them

I recommend "THE" Design Pattern book:
Design Patterns
by Eric Gamma et al

It's a great book written by GoF(Gang Of Four), read and re-read this one as the authors themselve suggest to .