A Genealogy of Control Structures The issue of program control structures has had a history of heated controversy. To put this issue on a solid footing, this paper reviews numerous theoretical results on control structures and explores their practical implications. The classic result of Bohm and Jacopini on the theoretical completeness of if-then-else and while-do is discussed. Several recent ideas on control structures are then explored. These include a review of various other control structures, results on time/space limitations, and theorems relating the relative power of control structures under notions of equivalence. In conclusion, the impact of theoretical results on the practicing programmer and the importance of one-in, one-out control structures as operational abstractions are discussed. It is argued further that there is insufficient evidence to warrant more than if-then-else, while-do, and their variants. CACM November, 1975 Ledgard, H. F. Marcotty, M. structured programming, control structures, goto statements, language design, PASCAL 4.2 5.24 CA751103 JB January 6, 1978 9:53 AM 2319 4 2709 2411 4 2709 2480 4 2709 2574 4 2709 2594 4 2709 2709 4 2709 2709 4 2709 2709 4 2709 2709 4 2709 2709 4 2709 2802 4 2709 2889 4 2709 2937 4 2709 2939 4 2709 2972 4 2709 2989 4 2709 3004 4 2709 3004 4 2709 3005 4 2709 3025 4 2709 3101 4 2709 3121 4 2709 3155 4 2709 1425 5 2709 2138 5 2709 2204 5 2709 2456 5 2709 2477 5 2709 2709 5 2709 2709 5 2709 2709 5 2709 2821 5 2709 3121 5 2709 1312 6 2709 308 6 2709 309 6 2709 2456 6 2709 2709 6 2709 2709 6 2709