Does anyone have a tool for converting old-style C programs to ANSI C, or vice versa, or for automatically generating prototypes?

Two programs, protoize and unprotoize, convert back and forth between prototyped and ``old style'' function definitions and declarations. (These programs do not handle full-blown translation between ``Classic'' C and ANSI C.) These programs are part of the FSF's GNU C compiler distribution; The unproto program (/pub/unix/unproto5.shar.Z on ftp.win.tue.nl) is a filter which sits between the preprocessor and the next compiler pass, converting most of ANSI C to traditional C on-the-fly.
The GNU GhostScript package comes with a little program called ansi2knr.
Before converting ANSI C back to old-style, beware that such a conversion cannot always be made both safely and automatically. ANSI C introduces new features and complexities not found in K&R C. You'll especially need to be careful of prototyped function calls; you'll probably need to insert explicit casts. Several prototype generators exist, many as modifications to lint. A program called CPROTO was posted to comp.sources.misc in March, 1992. There is another program called ``cextract.'' Many vendors supply simple utilities like these with their compilers.