Ball won't bounce off sides

Question

I've written some code to make the ball bounce off the edges and move diagonally. But the ball just disappears off the edge of the window! I've read elsewhere that I have to initialise the velocity variables outside the while loop, but I've done this and it still happens! The ball instantiates fine, it moves, but it just disappears off the edge instantly! I'm totally confused!
Here is my while loop:

        double velocity = drand48();
double velocityY = 2;

// keep playing until game over
while (lives > 0 && bricks > 0)
{
    // make paddle respond to mouse movement
    GEvent event = getNextEvent(MOUSE_EVENT);

    if (event != NULL)
    {
        if (getEventType(event) == MOUSE_MOVED)
        {
            double x = getX(event) - getWidth(paddle)/2;
            setLocation(paddle, x, 500);
        }


    }

    move (ball, velocity, velocityY);

    if (getX(ball) + getWidth(ball) >= getWidth(window))
    {
        velocity = -velocity;
    }
    else if (getX(ball) <= 0)
    {
        velocity = -velocity;
    }
    else if (getY(ball) <= 0)
    {
        velocityY = -velocityY;
    }   
}

Answer 1

I see your ball heading mostly down and off the window. You never test for down. Which ultimately is what you will need to detect the ball getting past the paddle. Remember that zero y for the window is at the top, and positive velocities well make the ball travel down and to the right. If you don't seed the random number gen then it will always do the same thing. For testing make velocity an hard number like 3 to see the ball go right and left.