CRunDec: A C++ package for running and decoupling of the strong coupling and quark masses. In this paper we present the C++ package CRunDec which implements all relevant formulae needed for the running and decoupling for the strong coupling constant and light quark masses. Furthermore, several formulae are implemented which can be used to transform the heavy quark masses among different renormalization schemes. CRunDec is the C++ version on the Mathematica package RunDec containing several updates and improvements.