VMS Help CC, Messages, SEQUENCEEXT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> allowing a comma operator is a language
                extension.

 Description    In this context the C standard does not allow the
                comma (sequence) operator.  Compaq C allows this
                syntax for compatibility with some other C compilers.
                Be aware that this syntax may not be accepted by
                other C compilers.

 User Action    If the intent is to use an expression that is not
                necessarily a constant expression, then enclose it in
                parentheses.  But if the intent of the declaration is
                to use a constant expression, then the comma operator
                cannot be used.