The examples which come with the compiler should show you some of the basics. Microsoft style defaults are different from linux and cygwin. If you examine the .obj files, using dumpbin /symbols, you would see that the Fortran would call CALC, rather than calc_. Also, if you haven't decided whether you are compiling with C or C++, that would be a useful decision to make. In C++, you would have to add extern "C" to the declaration of CALC. If you want ifort to use the linux style conventions, you need -Qlowercase -us. If you do that, you will not be able to use libraries built for the default convention. I think I saw a reply from Steve Lionel, but it seems to have been deleted.