How to find all possible functions of f with a given derivative.

Question

1. f'(x) = 2
2. f'(x) = sinx

Integrate each function. Remember that there can be an arbitrarcontant C added to each integral.

1. f(x) = x + C
2. f(x) = -cos x + C

We haven't learned integration yet. Is there any other way? Integration comes in the next chapter, I guess.