Procedures

 

A procedure, such as an intrinsic function, is an abstracted block of parameterised code that performs a particular task. Procedures should generally be used if a task has to be performed two or more times, this will cut down on code duplication.

Before writing a procedure the first question should be: ``Do we really need to write this or does a routine already exist?'' Very often a routine with the functionality already exists, for example, as an intrinsic procedure or in a library somewhere. (Fortran 90 has 113 intrinsic procedures covering a variety of functionality and the NAg fl90 Numerical Library contains over 300 mathematic procedures so there is generally a wide choice!)

As the use of Fortran 90 grows many useful (portable) library modules will be developed which contain routines that can be USE d by any Fortran 90 program. See World Wide Web Fortran Market.

If a procedure is to be written from scratch then the following guidelines should be followed:

• It is generally accepted that procedures should be no more than 50 lines long in order to keep the control structure simple and to keep the number of program paths to a minimum.
• Procedures should be as flexible as possible to allow for software reuse. Try to pass as many of the variable entities referenced in a procedure as actual arguments and do not rely on global storage or host association unless absolutely necessary.
• Try to give procedures meaningful names and initial descriptive comments.
• There is absolutely no point in reinventing the wheel -- if a procedure or collection of procedures already exist as intrinsic functions or in library module then they should be used.