CodeIgniter model method to update a record fails because of undeclared $id variable [closed]

I have an HTML table full of inputs populated by data in a database table. I generate a form for each row as a separate table, and a submit button for each. I want the update button to update only the row associated with the generated form.

If I remove this->db->where('id', $id); from the model, it updates all rows in the table with the same info. With the where() call present, nothing is updated.

VIEW

<?php foreach($log->result() as $row): ?>
<?=form_open('hq/update_entry');?>
    <table class="editLog">
        <tr>
            <td><?php 
                $data = array(
                    'name' => 'no',
                    'value' => $row->no
                );
                echo form_input($data);
                ?></td>
            <td><?php 
                $data = array(
                    'name' => 'date',
                    'value' => $row->date
                );
                echo form_input($data);
                ?></td>
            <td><?php 
                $data = array(
                    'name' => 'artist',
                    'value' => $row->artist
                );
                echo form_input($data);
                ?></td>
            <td><?php 
                $data = array(
                    'name' => 'title',
                    'value' => $row->title
                );
                echo form_input($data);
                ?></td>
            <td><?php 
                $data = array(
                    'name' => 'long',
                    'value' => $row->long
                );
                echo form_input($data);
                ?></td>
            <td><?php 
                $data = array(
                    'name' => 'lat',
                    'value' => $row->lat
                );
                echo form_input($data);
                ?></td>
                <td>
            <?php
                echo form_hidden('id', $row->id);
                $data = array(
                    'class' => 'updateSubmit',
                    'value' => '✚'
                );
                echo form_submit($data);
            ?></td>
        </tr>
    </table>
<?=form_close();?>

CONTROLLER

public function update_entry()
{
    $this->load->model('update_entry_model');
    
    if ($query = $this->update_entry_model->update()) {
        $this->index();
    } else {
        redirect('hq');
    }
}

MODEL

class Update_entry_model extends CI_Model
{
    public function update()
    {
        $data = array(
            'no' => $this->input->post('no'),
            'date' => $this->input->post('date'),
            'artist' => $this->input->post('artist'),
            'title' => $this->input->post('title'),
            'long' => $this->input->post('long'),
            'lat' => $this->input->post('lat')
        );
        $this->db->where('id', $id);
        $this->db->update('entries', $data);
    }
}