Hello there, have we met before? The name sounds familiar.
Agam, I have yet to see the exercise that works out BOTH at the same time, though I know push-ups work the pectorals and the back muscles, just to name a few... (Pushups are probably one of the most versatile exercises) But you can work the pectorals with pushups by simply widening your stance. As for the abdominals...there's always situps. But you probably want something more since a brain-dead gorilla would know that. You can always make the situps harder by using a more advanced stance or adding weights. Along with situps, you should do obliques to cover the oblique abdominals. Toe touches are also great for the abdominals; try hold the exerted position for 30-45 seconds. I'm actually gonna make some Youtube videos on some stuff I've picked up over the years that I think will be helpful so I'll definitely put some stuff up with pectorals and abs.
Btw, for stuff like this, you should post it in the "exericse specifics" forum.
While we're on pushups, a great variation that I've found is if you put your feet on one of those large stretching balls; it works your abs like nuts trying to keep your base steady. Though, heck, putting your toes on any slippery surface, like wearing socks on a wood floor, makes your abs work a lot harder to keep form while doing pushups. (I shouldn't have to point out that pushups are good for pecs, right?)