C-Fortran interface

I do not have experience of interfacing Fortran with C.. I mean exchanging and sharing data between C routines and Fortran routines linked together. I would appreciate some guidelines how to do that. Basically, assume the following common block is defined in a fortran routine called "m1505.f": COMMON/LEXP/DLEXP,TO,AINT That is the Fortran routine defined the common block named "LEXP" containing the three valiables DLEXP, TO, AINT Now assume that such a Fortran routine is linked to some C routines and some Tcl/Tk procedures through a GNUmakefile. How can I, from inside a C routine, access the content of the variable AINT in the common block LEXP ? Thank you in advance for any suggestion. Maura