Structured programming - Rule of thumb (2)

• Subroutines communicate with each other exclusively via parameters and function values (or via class and instance variables – see later) and not via shared, global data structures • A subroutine should also be documented as precisely as possible (ideally formally), in particular: • the effect mentioned above (»postcondition of the subroutine«) • the conditions that must be met for the subroutine to be able to achieve this effect (»precondition of the subroutine«)