[erlang-questions] Newbie Question about io:format

[Hakim Fajardo]

First, thank you because this is a great resource. 

Second, I started writing basic programs every day to improve my Erlang coding. I wrote a simple program that calculates the average of a list of numbers. But I keep getting this error about io:format.

prices([]) ->
    [],
    io:format("List is empty ~n");

%% determine number of items in the list to calculate average%%

prices(L) when is_list(L) ->
  Size = length(L),
  Sum1 = lists:sum(L),
  Av1 = Sum1 / Size,
  io:format("The average equals ~n", Av1).

Then..

Eshell V8.2  (abort with ^G)

1> L = [1,2,2,2,3,3,4].

[1,2,2,2,3,3,4]

2> c(standev).

{ok,standev}

3> standev:prices(L).

** exception error: bad argument

     in function  io:format/3

        called as io:format(<0.50.0>,"The average equals ~n",2.4285714285714284)

Why am I getting '**exception error:'?

Thank you, I hope this isn't too newbie a question.

[Dmytro Lytovchenko]

Because Erlang has no functions with variable amount of arguments (like for example in printf C/C++), args to io:format are passed as a list. So correct way to call it is:

io:format("Bla ~p~n", [Av1]).

Where ~p is to print any value, also there are more ways to format a value, consult the documentation page at http://erlang.org/doc/man/io.html#fwrite-1

_______________________________________________
erlang-questions mailing list
erlang-q...@erlang.org
http://erlang.org/mailman/listinfo/erlang-questions

[Richard A. O'Keefe]

On 21/02/17 10:15 PM, Hakim Fajardo wrote:
(simplified):

prices([]) ->
io:format("List is empty~n");
prices(L) when is_list(L) ->
io:format("The average equals ~n", lists:sum(L)/length(L)).
^^^^^^^^^^^^^^^^^^^^^^^

% man io
format(Format, Data) -> ok
Data = [term()]

The second argument of io:format/2 should be a list.

What part of the format says to expect a number?
What part of the format says how to print a number?

[Hakim Fajardo]

Thank you,

I understand now.

[Hakim Fajardo]

Thank you! I see now.