Question

I give it 0 and 400 and it returns me sometimes values above 400. That doesn’t make sense.

- (float)randomValueBetween:(float)low andValue:(float)high {
    return (((float) arc4random() / RAND_MAX) * (high - low)) + low;
}

that’s actually a snippet I found on the net. Maybe someone can see the bug in there?

Answer 1

The manual page for arc4random indicates that the returned value can be anywhere in the range valid for u int32 (i.e. 0 to (2**32)-1). This means you’ll want to divide by 0xFFFFFFFF, instead of RAND_MAX, which I would imagine is less (it is library dependant however, so you’ll have to check exactly what it is).

Your function should thus become:

- (float)randomValueBetween:(float)low andValue:(float)high {
    return (((float) arc4random() / 0xFFFFFFFFu) * (high - low)) + low;
}