Even if you don't actually use it as a compiler,
ftp://ftp.netlib.org/f2c/src, can be a useful tool when you're
interfacing (linking) Fortran and C.
See Generating Skeletons and Prototypes with
f2c for this purpose you only need retrieve and
src directory from the distribution, consult the
README instructions there for machine-specifics, and install the
f2c program on your path.
Something else that might be useful is
This is a fairly general tool which
can be used to generate interfaces for calling in both directions
between Fortran and C.
It can be used in
f2c mode with
g77--consult its documentation for details.