difference between c89 and c99

[Chad Perrin]

It has been years since I've worked with the C programming language at
all, and I've forgotten most of what little I knew then.  Now that I'm
starting to look into learning C (again-ish), for purposes of perhaps
contributing code to some FreeBSD projects, I find myself staring at
the available compilers in the base system for FreeBSD and wondering at
the differences.  Any information I can get on the subject would be much
appreciated.

For instance:

  What's the difference between c89 and c99?

  Is there any reason to avoid c*9 in favor of gcc (or vice versa) when
  working on FreeBSD projects?

Please don't necessarily limit yourself to these questions if/when you
choose to give me an answer.

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
Paul Graham: "Real ugliness is not harsh-looking syntax, but having to
build programs out of the wrong concepts."