how to input multiple values and data at the same time ?

PHP Code:

$id_surat = $this->db->query('SELECT surat.id_surat FROM surat ORDER BY id_surat DESC limit 1');
$id_user = $this->input->post(array('id_user')); 


I think you expect both these to return single value, I'm pretty sure both, or at least first, is returning either array or DB query result object.

For first line, you probably want to do something like this:

PHP Code:

$id_surat = $this->db->query('SELECT surat.id_surat FROM surat ORDER BY id_surat DESC limit 1')->first_row()->id_surat ;