Why is this code unable to bounce the ball

Question

In my code for breakout, the ball is unable to bounce up and down, though the same code works in bounce.c for bouncing the ball vertically!

Here's the main part meant for moving the ball:

while (lives > 0 && bricks > 0)
{
    // TODO
    double velocity = -0.5;
    move(ball, 0, velocity);

    // bounce off Y axis's edge of window
    if ((getY(ball) + getHeight(ball)) >= getHeight(window) || getY(ball) <=0)
    {
        velocity *= -1;
    }

    pause (10);
    GEvent event = getNextEvent(MOUSE_EVENT);
    if (event != NULL)
    {
        if (getEventType(event) == MOUSE_MOVED)
        {
            double paddleX = getX(event) - (PADDLE_WIDTH / 2);
            setLocation (paddle, paddleX, HEIGHT - 35);
        }
    }
}

This is only the first baby step I've taken towards this problem, and have failed. I am quite unhappy, please help me find errors!

This code though functions all right in the bounce.c program to bounce the ball between up and down, but when I place this code in the breakout.c file, it doesn't work. The ball just moves up and escapes the field of view and well, disappears...

Answer 1

Converting the code to pseudo code might help to reveal the problem:

loop while lives > 0 and bricks > 0

    set velocity to -0.5

    move the ball in the y axis by the velocity

    if the ball touches the top edge or bottom edge

        reverse the velocity

    handle mouse input

    etc

Note that regardless of what happens to the velocity in a collision, the first line in the loop always sets velocity back to 0.5.