The textbook is intended to be used in the computer science course of "Object-oriented programming in C++." It contains all the information needed for completing assignments and labs. The textbook consists of 5 parts. At first we consider the possibilities of C++, which did not exist in the language C and which don't refer directly to the notion of classes, in particular, stream input/output, operators of dynamic allocation of memory and setting it free, overloading of functions, template functions. Further, we passed over from the notion of structure in the language C to the notion of the class. We described the operations of the construction of the class and its elimination, static members of the class, friendly functions, interface and realization of the class, overloading of operators for the objects of the given class, templates of classes and friendly ones. We have also considered means of using created classes (aggregation and inheritance) for the extending possibilities of existing classes and the notion of the base and derivative classes, multiple inheritance, building of the hierarchy of classes, usage of virtual functions, abstract classes, polymorphic functions, virtual inheritance. In every part of the textbook we have given examples of programs with comments, demonstrating suggested theoretical material. Every part ends with the questions for self-control and tasks for independent work with the demonstrated programs. At the end of the textbook we have introduced the mandatory assignments for the course OOP in C++. In order to help the students the textbook demonstrates codes of similar programs for all the types of assignments. This textbook is intended for educational purposes.