On program control structure

Abstract

The syntax of the DO-WHILE is revised so as to distinguish the semantics of logical control of iteration from those of site of test within the scope of the DO. The corresponding control graph (flowchart subdiagram) is shown to be a combination of previously used alternative forms. An indentation scheme is proposed in which the indentation rules are identical for both iterative and conditional statements. Furthermore the rules as given are identical for any programming language, whether it is a lower level language which requires hand coded book-keeping statements or some ideal language in which all loop control is provided for in the syntactic forms. The minimal sufficient set of program control structures is augmented with forms for the convenience of human program writers and readers. These forms all share common indentation rules corresponding to those used for the DO-WHILE and IF-THEN-ELSE. Last a form is provided for handling error conditions, POSIT-QUIT-ADMIT in which multiple QUITs are permitted. The indentation rules are compatible with the preceding rules.