The clean termination of iterative programs

Summary The paper is devoted to a program-correctness concept which captures partial correctness, termination (nonlooping) and clean termination (nonabortion). The underlying proof method offers a one-stage proof of all the three properties. This method is proved consistent and algebraically complete. It is first discussed for the general case of arbitrary possibly nondeterministic iterative programs. Next, this case is restricted to arbitrary deterministic iterative programs and finally to structured programs. The presented approach is compared with partial correctness, total correctness and weakest precondition methods. The concluding example shows the verification of an arithmetical program in machine-bounded arithmetics. As a side effect of the verification procedure one finds input boundary conditions which guarantee clean termination.This paper was prepared when the author was visiting the Department of Computer Science of the Technical University of Denmark in Lyngby.