Opengl make "AI" paddle move up and down

Question

I'm a bit of an openGL/programming noobie so I'm trying to make an "AI" for the right paddle. I know this isnt the proper way of doing it, what I SHOULD be doing is making it follow the ball. But right now I'm just trying to make it perpetually move up and down. I can't figure out how to do it, trying to use If loops like

if (paddle.pos[1] > 1){ paddle.pos[1] = paddle.pos[1] - delta}

I set delta to something like 0.01, 1 is the top of the screen. Obviously this isnt right because as soon as it goes down below 1 it goes up again, but I'm trying to do something like it.

2nd question - How do you move the ball from 0,0 when it starts? Kind of the same problem, am using if statements with the x values but thats definitely not right.

This is using C by the way.

Answer 1

Try something like this to make pos repeatedly go from 0 to 1 and back to 0:

// Initialize.
float pos = 0.0f;
float delta = 0.01f;

// On every update.
pos += delta;
if (pos > 1.0f) {
    pos = 1.0f;
    delta = -delta;
} else if (pos < 0.0f) {
    pos = 0.0f;
    delta = -delta;
}

The key here is that you invert the sign of your increment each time you reach one of the end positions.