I really want a flat stomach

exercise any way you want, it makes all the difference. try eatin smaller portions more often in the day (like 4-6 small meals (250-300 calories each), it activates your metabolism, which in turn makes oyu lose weight. eat A LOT OF fruits and vegs, those will fill you up nicely and make you less hungry. any kind of beans, yogourt and nuts, seeds and whole grains are also really good for losing weight.

I was pretty overweight younger like 40 lbs overweight , now im 21 at 115 feelin fine. this is what i did to lose the weight.

mostly walking, bicycling, dancing and eating right did the job.

good luck.

OH AND ALSO, for belly fat specifically, dancing helps soooooooooooo much. try concentrating on dance moves with your belly and hips. my hips look so fine now =D. people tell me i have a fabulous waist line.  10-20 sit-ups a day can do wonders as well.