let freq str =

  let len = String.length str in
  let freqs = Array.make 256 ('*', 0) in

  for i=0 to (len-1) do
    let tempchar = String.get str i in
    let asciinum = int_of_char tempchar in
    let ch = freqs.(asciinum) in
    freqs.(asciinum) <- ((char_of_int asciinum),(snd ch)+1);
  done;

  freqs
;;