program CumulDev;
(* Cumulative standard deviation *)

  unit SAMPLE: class;
  var
    n: integer,
    sum: real,
    sum_of_squares: real;

    unit add: procedure (p: real);
    begin
      n := n + 1;
      sum := sum + p;
      sum_of_squares := sum_of_squares + p * p
    end add;

  begin (* constructor *)
    n := 0;
    sum := 0.0;
    sum_of_squares := 0.0
  end;

var
  test: arrayof real,
  s: SAMPLE,
  i: integer;

  unit deviation: function (s: SAMPLE): real;
  var
    quot: real;
  begin
    quot := s.sum / s.n;
    result := sqrt(s.sum_of_squares / s.n - quot * quot)
  end deviation;

begin
  array test dim (1 : 8);
  test(1) := 2; test(2) := 4; test(3) := 4; test(4) := 4;
  test(5) := 5; test(6) := 5; test(7) := 7; test(8) := 9;
  s := new SAMPLE;
  writeln("N ITEM AVG   STDDEV");
  for i := 1 to upper(test)
  do
    call s.add(test(i));
    write(i: 1, "  ", test(i): 3: 1, " ");
    write(s.sum / i: 5: 3, "  ");
    writeln(deviation(s): 5: 3);
  od;
  kill(s);
end CumulDev.