The ``output C code'' phase ``unparses'' the AST back to C code, leaving the result in file(s) with names related to the input file(s). For example, entering cbz -c-code foo.c bar.c will parse, then unparse foo.c and bar.c, leaving the results in foo.p.c and bar.p.c. This is the phase you want to run after you have done some transformations on the C code, so that your result will be saved in a file.