Thanks for your reply, it's exactly what I asked for! By the way, you asked for details that I should have specified earlier; I'll go in order:
First, I'm right now only having some ideas for a game that would require to store some data in order to resume the game after opening the app again; then I also want the game to support multi-touch. About the game engine, I want to write it by myself, but I'm proably go with a simpler solution for the graphic engine.
I have the basics of game programming (drawing, input poll, etc): I learned how to program games with Allegro, that is literally: "Allegro Low LEvel Game ROutines". To be more specific: it's a free C and C++ library, which recently got support for Android.
Then about what to choose... Of course I already considered going with the official Android development package, but it's probably overkill, not to mention that I don't posses a PC with that meets the system requirements.
About the engines, I've got my interest on these ones:
Allegro,
SFML,
SDL, and of course Unity3D.
So I have two questions now: is multi-touch support available from everywhere, or is it necessary to stick to specific software environments? Second: how do I protect my software from being stolen?