How to loop though an array plpgsql?

I need to loop though an input array, but can't figure out how to do it,
the docs aren't really clear on this.

Something like this:

CREATE FUNCTION update (_id INTEGER[])
RETURNS VOID AS
$$
BEGIN
 FOR i IN SELECT _id LOOP   INSERT INTO table VALUES (_id[i]); END LOOP;

END;
$$
LANGUAGE plpgsql;

Anyone know the correct loop syntax?

schu