no output display in dropdown list

Code:

<select name="staff" id="staff" required>
<option value="">Select Staff</option>
<?php

while($row_subject = mysql_fetch_array($query_subject)) {
?>
<option value="<?php echo $row_subject['deo_code'];?>  
($this->input->post('staff') == $row_subject['deo_code'] ? ' selected' : '') ><?php echo $row_subject['deo_code']."-".$row_subject['deo_name'];?></option>
<?php } ?>
</select>