can't understand warnings in simple Pl/SQL function

I am using Oracle 10g with SqlDeveloper. When I execute the follow开发者_如何学运维ing code, it says

"FUNCTION wafadar compiled Warning: execution completed with warning"

create or replace function wafadar
return varchar2(10)
is

cursor c1 is
SELECT employee_id,first_name FROM employees where department_id=50 ;

begin
  for i in c1
  loop
    dbms_output.put_line(i.first_name);
  end loop;
  return 'hello';
end;

SHOW ERRORS at the end is also not showing the warnings. Why are the warnings there ?

Errors!

At first, you should care about errors, and I bet you have one on the return clause of your function (you can't specify the size of the "varchar2".

Warnings

Did you look for "warning" in the manuals? http://download.oracle.com/docs/cd/E11882_01/appdev.112/e17126/errors.htm#LNPLS00711

How to see warnings(enable categories you need)

alter function wafadar compile plsql_warnings='ENABLE:ALL' reuse settings

Check:

select plsql_warnings
from   user_plsql_object_settings ps
where  ps.name = 'WAFADAR'

Your warnings:

Client tools like sql*plus or Sql Developer(if supported):

 show errors

or

select *
from   user_errors ur
where  ur.name = 'WAFADAR'

NAME                           TYPE           SEQUENCE       LINE   POSITION TEXT                                                                             ATTRIBUTE MESSAGE_NUMBER
------------------------------ ------------ ---------- ---------- ---------- -------------------------------------------------------------------------------- --------- --------------
WAFADAR                        FUNCTION              1          1          1 PLW-05018: unit WAFADAR omitted optional AUTHID clause; default value DEFINER us WARNING             5018

Finally, I suggest you to read a little bit of:

1. How to ask: http://www.catb.org/~esr/faqs/smart-questions.html#before
2. http://download.oracle.com/docs/cd/E11882_01/appdev.112/e17126/toc.htm
3. All the "oracles" are here: http://tahiti.oracle.com/
4. Sql developer oracles(if you want to use it!): http://download.oracle.com/docs/cd/E11882_01/doc.112/e12152/toc.htm