On the capabilities of while, repeat, and exit statements

ABSTRACT

A well-formed program is defined as a program in which loops and if statements are properly nested and can be entered only at their beginning. A corresponding definition is given for a well-formed flowchart. It is shown that a program is well formed if and only if it can be written with if, repeat, and multi-level exit statements for sequence control. It is also shown that if, while, and repeat statements with single-level exit do not suffice. It is also shown that any flowchart can be converted to a well-formed flowchart by node splitting. Practical implications are discussed.

REFERENCES

• 1: Knuth, D.E., and Floyd, R.W. Notes on avoiding'GO TO' statements, blf. Proc. Letters I (1971), 23-31.
• 2: Edward A. Ashcroft , Z Manna, The translation of ''go to'' programs to ''while'' programs, Stanford University, Stanford, CA, 1971
• 3: Wulf, W.A. Programming without the GOTO. IFIP 71 TA-3-84.
• 4: Ianov, Y.I. The logical schemes of algorithms. In Problems of Cybernetics, Vol. 1, English ed., Pergamon Press, New York, 1960, pp. 82-140.
• 5: John E. Hopcroft , Jeffrey D. Ullman, Formal languages and their relation to automata, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1969
• 6: McKeeman, W.M., Homing, J.J., and Wortman, D.B. A Compiler Generator. Prentice-Hall, Englewood Cliffs, N.J., 1970.
• 7: Harary, F. Graph Theory. Addison-Wesley, Reading, Mass., 1968.
• 8: Cocke, J., and Miller, R. Some analysis techniques for optimizing computer programs. Proc. 2nd Int. Conf. of Syst. Sci., Hawaii, Jan. 1969.
• 9: Elspas, B., Green, M.W., and Levitt, K.N. Software reliability. Computer 4 (Jan. 1971), 21-27.
• 10: William A. Wulf, A case against the GOTO, Proceedings of the ACM annual conference, p.791-797, August 01-01, 1972, Boston, Massachusetts, United States [doi>10.1145/800194.805861]
• 11: Lyons, T., and Bruno, J. An interactive system for program verification. Tech. Rep. No. 91, Dept. of E.E., Princeton U., Princeton, N.J., 1971.

INDEX TERMS

Keywords:
exit statement, flowchart, go to statement, node splitting, repeat statement, software reliability, well-formed program, while statement