Unless you are writing code that must be recompiled on a system
where ANSI C is not available, it is recommended that you use the
ANSI mode of compilation for your new development. It is also recommended
that you use ANSI mode to recompile existing programs after making
any necessary changes.
Because an ANSI-conforming compiler is required to do more
thorough error detection and reporting than has been traditional
among C compilers in the past, you may find that your productivity
will be enhanced because more errors will be caught at compile time.
This may be especially true if you use function prototypes.
If you do not specify the mode of compilation, beginning with
the HP-UX 10.30 operating system release, it defaults to -Ae.