Variable Name Conventions

[Jeffrey Adam Gordon]

I have seen C source with at least three different types of variable
names.  Some are just 'var' while others are either '_var' or '__var.'
What I'd like to know is:  is there any convention for using
underline (and for that matter, CAPS) in C variable/function/structure
names.  Does anyone have a neat system they like to use when, say,
defining typedefs (such as "all typedefs will end in '_t') or
pointers (like '_p').

I think you get the picture.  Thanks to all in advance.

- jag -