Intel fortran-80 FORTRAN Coding, Functions And Subroutines, GO TO Statement, Crossing Unit Lines

Programming Guidelines FORTRAN-SO

This is just a 'starter' list. Certainly, any experienced programmer could add to this checklist. Rereading such a list frequently, like rereading programming manuals, is a good way to refresh or reconfirm programming knowledge.

7.2 FORTRAN Coding

Section 7.1 lists some general programming considerations. When coding in FOR- TRAN specifically, other points should be kept in mind.

7.2.1 Functions And Subroutines

The first point has already been made in Chapter 5, but is worth repeating. Use functions and subroutines in a program wherever it makes sense to do so. First of all, they reduce the amount of coding to be done, saving time and reducing the chance of error. They also save processor memory by allowing shorter programs. And, most importantly, they break a program into units that can be separately pro- grammed and debugged and that also clarify its logical structure, making it easier to understand.

7.2.2 GO TO Statement

The GO TO statement should be used only when necessary. The ability to jump around at will within a program can be a strong temptation to neglect logical plan- ning. No painter would worry about painting himself into a corner if he could escape by simply shouting 'go to exit.' When the GO TO seems necessary, consider first whether an alternative solution that would improve the logical structure of the pro- gram has been overlooked.

7.2.3 Crossing Unit Lines

The ability to divide a program into subprograms is a major benefit of FORTRAN. It also has some potential pitfalls. Be careful when using global variables, external procedures, and variables whose values have been computed outside the current pro- gram unit! Take advantage of the capability provided by common memory, but be aware of the interaction among all the program units that reference common memory!

7.2.4 Computing Variables And Constants

Complex calculations can frequently be simplified by breaking them into several steps and computing intermediate variables. This is particularly true if such variables are used several times after their value has been computed. Program execu- tion time can be reduced by using intermediate variables and the program is general- ly more readable. Like most programming tools, however, the use of intermediate variables can be abused and requires good judgement.

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