GENERATING STRUCTURED FLOW DIAGRAMS: THE NATURE OF UNSTRUCTUREDNESS.

Abstract

Various methods have been put forward for converting an ″unstructured flow diagram″ into an equivalent ″structured″ one . This paper examines the basic flow diagram substructures, the presence of which in a flow diagram causes the flow diagram to be unstructured, and proves that these are the only structures which lead to unstructuredness. While the basic structures of structured programming are sequence, selection (if-then-else) and repetition (do-while), the five basic structures which lead to nondecomposability are abnormal selection path, loop with multiple exit points, loop with multiple entry points, overlapping loops and parallel loops.