The book summarizes many years of experience in programming training at ETN, Zurich. It successfully combines three facets characteristic of professional programming - science, art and engineering. It is primarily aimed at students studying in the field of information technology and their teachers, but is of undoubted interest to all programmers who create a high-quality software product. The textbook outlines the basics of object-oriented programming (OOP). Particular attention is paid to the correctness of programs through the introduction of contracts - preconditions, postconditions of class methods, class invariants.