The paper deals with a special way of the construction of the boundary conditions for the compressible gas flow. The solution of the Riemann problem is used at the boundary. It can be shown, that the unknown one-side initial condition for this problem can be partially replaced by the suitable complementary condition. Authors work with such complementary conditions (by the preference of pressure, velocity, total quantities,...) in order to match the physically relevant data. Algorithms were coded and used within the own developed code for the solution of the Euler, NS, and the RANS equations, using the finite volume method. Numerical example shows superior behavior of these boundary conitions in comparison with some other boundary conditions. and Obsahuje seznam literatury