And ehm second question, so I wont start two threads.[/quote]
The first part of the question would be better suited in Business And Law, while the second one should stay here. It's best to only ask one question per topic, especially when they don't touch on the same domains.

Hi. I'm wondering if it's legal to copy the gameplay of a classic game, such as Snake.I don't know much about copyright issues.I'm trying to make a clone of it. The main character is not a snake, and he's not looking for food like in the original game.It's body does grow when he collides with the "object of desire " and he is destroyed if he goes out of boundaries or hits its own "tail" or the obstacles.I'm asking because I want to present my project in a contest.It will not be commercial.[/quote]
My understanding is that you would in general be treading on legal fire here, the boundaries between "ripping off game IP" and "reusing original but non-copyrightable gameplay elements" could be very blurry. Fortunately, you are lucky, because the Snake concept itself is not (and cannot be) copyrighted*. So you are free to create your own variant, as long as you don't rip off names, art assets or explicit rules from other snake versions. And to be fair, if it's not going to be commercial, I don't think anybody will reject your game or get you in trouble at the contest, except perhaps overzealous judges. I wouldn't worry about it. After all, if the only reason you are making the game is for the contest, and it is actually copyrighted, it might actually fall under fair use.

* It could, however, be patented, in the USA at least, considering the sad state of the patent system, but I can't find such a patent.