My only advice is to not name it asteroids if you publish or distribute it. Allegro got in trouble for having their demo game A5teroids that comes with the library because it was too close to Asteroids. Now they have it renamed.
Anyway, I have made a lot of changes, and I think improvements, to mine. If anyone has the time, would you mind compiling it and telling me what you think of the gameplay. I am not so happy with the speeds and acceleration but am not sure exactly what to change.
It is an eclipse project so you can just import to eclipse, else you need to link
-lSDL -lSDL_image -lSDL_gfx -lSDL_ttf
Each object, ship.cpp, stroid.cpp, projectile.cpp have an update function that takes a delta time. These are where the velocity and position changes are handled.
Variables are defined in ship.cpp init, or stroid.cpp projectile.cpp ctors