I need help with collision code. I want to keep the player from falling through floors, pretty much. Help?

EDIT: Okay, I’ve got some good collision detection, but there’s something wrong with my moving code.

bool checkCollision(SDL_Rect &movable, double &vx, double &vy, SDL_Rect solid, bool move) {
int moveLeft = movable.x;
int moveTop = movable.y;
int moveRight = moveLeft + movable.w;
int moveBottom = moveTop + movable.h;

int solidLeft = solid.x;
int solidTop = solid.y;
int solidRight = solidLeft + solid.w;
int solidBottom = solidTop + solid.h;

int clipLeft = max(moveLeft, solidLeft);
int clipTop = max(moveTop, solidTop);
int clipRight = min(moveRight, solidRight);
int clipBottom = min(moveBottom, solidBottom);

if(clipLeft == clipRight || clipTop == clipBottom)
return false;

if(!move)
return true;

int clipWidth = clipRight – clipLeft;
int clipHeight = clipBottom – clipTop;

if(clipWidth solidX) {
// moving to right
movable.x += solidRight – moveLeft;
} else {
// moving to left
movable.x -= moveRight – solidLeft;
}
} else {
// moving along y axis
vy = 0;
int moveY = moveTop + movable.h / 2;
int solidY = solidLeft + solid.h / 2;
if(moveY > solidY) {
// moving to bottom
movable.y += solidBottom – moveTop;
} else {
// moving to top
movable.y -= moveBottom – solidTop;
}
}

return true;
}

Please help! If you’re interested in seeing what’s happening, here’s the program: http://files.chocoboheaven.com/uploads/Guests/files/85267_PaintWorld.zip