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DCL: MATH1: Summary: FORTRAN77 Standard

1.5.10 COMMON Statement

Compared to the EQUIVALENCE statement in the previous section that combines variables in a single program, a COMMON statement combines variables in different program units (such as subroutines).

In the early FORTRAN, delivery of data by arguments was a time-consuming process, so in the past, there was an overuse of COMMON statements for delivering data from the main program to the subroutines. However, at the present, the time is takes for data delivery by the two methods are nearly the same. However, the COMMON statement has the disadvantage of making it unclear as to which subroutine the value had been assigned to. Therefore, to improve readability, the user is advised against using a COMMON statement for delivering data to the subroutine.

In DCL, arguments are used for data delivery to the subroutine instead of a COMMON statement, unless there is a special need (such as securing work area).