This chapter steps out of OpenFOAM and presents short course on some aspects of C++ needed for understanding following chapter on thermodynamic library in OpenFOAM. If reader is proficient with C++ and has knowledge of macros, classes (including inheritance) and templates, this chapter can be skipped. We will discus these topics only on very eclectic basis and not in full depth to keep the text from bloating. The text also assumes some basic knowledge of C++ language (or similar). Focus will be on concepts, not on syntactic details.