Short answer: No.
Long answer: You cannot "spot reduce" with exercise. To flatten your stomach, you need to reduce body fat through diet. Exercises like crunches will strengthen your abs but not make them flat.
Report from an insider: A research from by the University of Mass in 1984 proved that after doing thousands of sit-ups or crunches every day for consecutive 27 days, there wasn't any significant reduction to belly fat.
So why am I still doing it like crazy? (I do about 100-300 crunches a day.) This is because abdominal crunches can help flatten abs, but only in combination with cardio and a healthy diet. A fat person can have the strongest abs in the world, but if he or she has a horrible diet, then you will never see a flat stomach or six pack.
All of the crunches in the world will not get you firm if you have belly fat on top of it! Cardio intervals (e.g. walking, running, bike riding, swimming or hiking) are necessary, as well as toning all parts of your abs, such as obliques.
You should probably do some weight-training, too, as that will help your body burn calories and fat efficiently, ergo help you keep your tummy flat while exercising those specific muscles. Drinking lots of water will also help you burn up to 100 calories a day.