Integration is one of the two basic operations in calculus and since it, unlike differentiation, is non-trivial, tables of known integrals are often useful. This page lists some of the most common antiderivatives; a more complete list can be found in the List of integrals.
We use C for an arbitrary constant of integration that can only be determined if something about the value of the integral at some point is known. Thus each function has an infinitude of antiderivatives.