How to get values from unchecked checkbox

I am working on an attendance reporting page.Here i am creating a dynamic checkbox with content from db.Now I can store the checked student(present) students detail i also want to store the absent student.I order to do that i want a hiden field or something for get the unchecked students detail please anyone help me to do that.

<form name="myform" action="" method="post">
<div class="checkbox">
<table border="1" cellspacing="2" cellpadding="5" summary="">
<?php while ($row = mysql_fetch_assoc($res)){?>
<tr><td> <input type="checkbox" class="input" id="input<?php echo $row['st_id']; ?>"  name="student[]" value="<?php echo $row['st_id']; ?>" checked="checked"   > <?php echo $row['st_name'] ; ?> <label for="input<?php echo $row['st_id']; ?>"></label><input type="text" name="absent" value="0"/></td>
</tr>
<?php }?>
</table>
<input type="submit" name="submit" value="submit"/>
</div>

PHP code

    <?php   
$res = mysql_query("SELECT * FROM `student_info` WHERE `sem`='$selsem'");   
if(isset($_POST["submit"]))
{
    //Here goes array
    for($i=0;$i<count($_POST['student']);$i++)
    {  
        $id=$_POST['student'][$i];
        echo $id;
        $check=1;
       mysql_query("insert into manage_attendance(st_id,date,sem,period,subject,status) values('$id','$seldate','$selsem','$selperiod','$selsub','$check')");
    }
}
?>