(* Returns a char from stdin, or ^D if EOF              *)
let get_char () =
  try 
    (input_char stdin)          (* read a character     *)
    with End_of_file -> '\004'  (* assume ^D marks EOF  *)
;;

(* Returns # chars read (including '\n')                *)
let rec count_chars () =
   let c = (get_char ()) in     (* get a character      *)
     if (c = '\004') then 0     (* if EOF then 0 chars  *)
     else 1+count_chars()       (* else read more chars *)
;;

print_int ( count_chars () ) ; print_endline ""
;;