pl/pgsql and controling loops

so are they both correct ?
comming from .NET/C++ world, usually we use '==' or '!=', so i expect that correct ones are '==' and '<>'.

moreover, when i check if the returned value "ret_email" from SELECT email INTO ret_email FROM tmp_newsletterreg WHERE tmp_usr_id = id_session;
i want to check if it is empty or not, so i do IF(ret_email <> '' ) THEN... but it does not work... every time it enter in the loop, even if it is empty string.

where is the problem ?

thx.