Eating light but healthily is better for dancers. Lots of vegetables, fruits, proteins, carbohydrates and foods containing those nutrients are all what a dancer needs 

Eating foods high in complex carbs are better for the long term energy while dancing. 

Keeping hydrated throughout the day is always important. 

What exercises they do: Dancers do a lot of cardio and stretches when they exercise. These exercises usually involve some sort of dancing.