Control Constructs

Abstract

By the 1970s there was widespread agreement among software professionals that code that relies on GO TO statements is generally harder to understand and maintain than code without GO TOs. But all of the popular Fortran implementations of the day required heavy use of GO TO statements since they lacked even such basic control structures as IF-THEN... END IF and WHILE. To overcome this weakness, a number of organizations independently developed computer programs known as “structured programming precompilers” (or “preprocessors”). The programmer then interspersed statements such as IF-THEN, CASE, WHILE, and REPEAT UNTIL with traditional Fortran code, and the precompilers translated the mixture into ordinary Fortran. The resulting translation was then compiled in the usual way. However, these precompilers were incompatible with one another, and when the FORTRAN 77 implementations became available in the 1980s, the structured programming precompilers faded away. Nevertheless, the precompilers have had a lasting influence on the thinking of those who used them and on the design of subsequent versions of the language, including Fortran 90.