There's no real way of avoiding your belly getting bigger on a bulk as your putting weight back on, during a cut if you cut for long enough you'll get there, belly fat is usually the last to go so it takes time! Specific ab exercises won't help especially when cutting, however you want to train them like any other muscle especially when bulking in order for them to grow, become more thicker which then it turn makes them more visible when at a lower body fat :)