On the capabilities of while, repeat, and exit statements

  • Authors:
  • W. W. Peterson;T. Kasami;N. Tokura

  • Affiliations:
  • Univ. of Hawaii, Honolulu, HI;Osaka Univ., Osaka, Japan;Osaka Univ., Osaka, Japan

  • Venue:
  • Communications of the ACM
  • Year:
  • 1973

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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.