if i do like 200 situps in the morning, afternoon, and night with good nutrition like greens almonds potatoes etc will that help for a stronger core and abs?
you will not build mass by doing that many situps you have to schedule your workout to build muscle. If you over work yourself by doing to much working out you wont give your muscles time to heal. when you workout you tear your muscles then they heal filling the tears with scar tissue making them bigger and harder. Hope this helps.
Yes, but don't use sit ups as your only core exercise. Do planks; front and side. Also do leg raises, bicycles, etc. You want to work your lower back also for core strength
Situps are bad because when you complete a rep you put a lot of strain on your neck
Doing Crunches works mostly your upper abdominals so try doing diffrent core exercises
Planks
Reverse Crunches
Moutain climbers
Oblique twist
Obliquq Crunches
And for an overall Ab workout do Rotation exercises with a medicine ball the bests are
Seated Russian Twist
Corkscrews
The secret to best abs are stripping the fat off your belly by doing cardiovascular exercises
and a good diet to not exceeding your daily caloric intake