Hey,
I am a c++ /allegro 5 programmer...coding need a team ,and if you are not in a team it will take a lot of your time . So what I say let's share our classes and what we have done ,so other game developer will not need to rewrite the same object...I mean by that someone give the particle system class other one give button class,collision functions,jump functions,fire functions,text box class and like that things ...after that the progression of the programming will increase a lot and we will have more time for graphics design and the story and that other things.

Okay of course I said that idea so I should to start first :

my classes :

game class. (event queue ,event ,timer ,inputs register function...)
page class.
button class.
text box class (input box).
text class.
timer class.
check box class.

Is it Monday already?

Game objects are very specialized. You may use x, y, for your objects, but I may use x, y, and "height" for game to denote drawing order. So using that alone, I'm going to have to inherit from your class and change the object handler, and the drawing I'm going to have to write myself anyway.

I'm not saying don't do it. But many of the things that can be reused already exist in better libraries than we could ever produce in passing. Just because code exists doesn't mean you should use it because it can have bugs you don't know about, and functionality you don't fully understand--because random code is not held to the same standard as library code with clearly defined interfaces and encapsulation.

gezegond made a good point about just make your code open-source and if anyone sees something they like, they can re-use it and send you a thank you letter.

While I'm not an employed professional programmer yet (give me a couple months), in my experience, the only things I reuse are standardized, tested libraries with defined APIs, existing proven codebases (what I'm working on in the first place), and small, concise implementations of known algorithms (a single function/object implementing FFT, etc). If you're not careful what you bring in, you open pandoras box for errors that you will spend weeks trying to find. And random code that I write for my hobby games is definitely not subjected to rigorous quality control--and that's me! I know me, I know even less about a stranger across the internet.

To a certain extent, a component-oriented design, instead of the classical object-oriented allows this more.