Reserved Words

  In most computer languages there is a long list of words which are reserved by the system and cannot be used as symbolic names: Cobol programmers, for example, have to try to remember nearly 500 of them. In Fortran there are no reserved words. Some Fortran keywords (for instance DATA, END, and OPEN) are short enough to be perfectly valid symbolic names. Although it is not against the rules to do this, it can be somewhat confusing.   The names of the intrinsic functions (such as SQRT, MIN, CHAR) are, technically, local names and there is nothing to prevent you using them for your own purposes, but this is not generally a good idea either. For example, if you choose to use the name SQRT for a local variable you will have more difficulty in computing square-roots in that program unit. It is even more unwise to use the name of an intrinsic function as that of an external procedure because in this case the name has to be declared in an EXTERNAL statement in every program unit in which it is used in this way.