Answer 1

If it is only the motion of a ball bouncing to a straight wall like in pong, you could do it easy by separate x direction and y direction of the ball and just multiply on of these by -1.

short example(not tested only for explanation):

int [2] ballpos = {12, 24};
int [2] ballvelo = {-1, -3};

void updateBallPos(&ballpos[2], &ballvelo[2]){

ballpos[0] += ballvelo[0];
ballpos[1] += ballvelo[1];

}

void reflectBallX( &ballvelo[2]){

ballvelo[0] *= - 1;

}
void reflectBallY( &ballvelo[2]){

ballvelo[1] *= - 1;

}

In main you can call updateBallPos periodically (every 20 ms e.g.). If an collision with a wall accured you just have to call the right reflect function. Hopefully that helps you.