g77 offers several extensions to FORTRAN 77 language that f2c doesn't:
FORMATstatements (such as `FORMAT(I<J>)', where `J' is a
libU77(Unix-compatibility) library, with routines known to compiler as intrinsics (so they work even when compiler options are used to change the interfaces used by Fortran routines)
g77 also implements iterative
so that they work even in the presence of certain “extreme” inputs,
However, f2c offers a few that g77 doesn't, such as:
It is expected that g77 will offer some or all of these missing features at some time in the future.