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

 Message        This integer constant value will be given the type
                unsigned long int.  This is compatible with the C89
                standard and older compilers.  The C99 standard
                requires this to be a signed long long int.

 Description    With the introduction of the long long int type, the
                C99 standard changed the rules for how the type of
                certain integer constants are determined.  Unsuffixed
                decimal constants which are too large for long int,
                but could fit in an unsigned long int are given the
                type long long int in C99.  Prior to C99 these would
                be given unsigned long int type.

 User Action    Be aware of this difference.