C Flowcharter Wanted

[Scot Mcintosh]

I'd like to find a freeware program that will accept C source input
and produce a flowchart from it.  By flowchart I mean the things
with lines and boxes, not a structure diagram or call-tree. It
would be nice if it ran on either a Sun or IBM PC compatible,
and source code is a must, since I'd like to tailor it to my 
needs.  Anybody know of a good one?  I
will summarize and post any responses.  Thanks.