My sister she is always asking me what are the best exercise she can do to get a flat stomach. I have recommended my favourite exercise, running but she refused, she wanted an exercise she can do indoors.
I researched around the internet and these were what I found
1. Good old sit ups
2. Bicycle exercise
3. Exercise Ball Crunch
4. Full vertical crunch
5. Plank on elbows and trunk, it won’t trim your tummy but it will give you a strong tummy
Other tips for a flat stomach
1. A good diet, cut on those calories
2. Stay hydrated.