Why is that My PHP records not being INSERTED

Why is that My PHP records not being INSERTED

Good Day!
Guys can you help me to check why my is it that i cannot insert records
using chekbox option on table..
Please Help..
Here's My Code...
--ADDING Subject Load for Teacher HTML Form-- (studsub.php)
<form action="setsubject.php" method="post">
<?php
include('../connect.php');
$id=$_GET['id'];
$result = mysql_query("SELECT * FROM student WHERE id='$id'");
while($row = mysql_fetch_array($result))
{
//$course=$row['course'];
//$year=$row['yearlevel'];
//$section=$row['section'];
$idnumber=$row['idnumber'];
echo '<br/>';
echo $row['lname'].", ".$row['fname'];
?>
<input type="hidden" name="studidnum" value="<?php echo $rows['idnumber']?>">
<?php }
?>
<br/><br/>
<label for="filter">Filter</label> <input type="text" name="filter"
value="" id="filter" />
<table cellpadding="1" cellspacing="1" id="resultTable">
<thead>
<tr>
<th style="border-left: 1px solid
#C1DAD7"><label>Assign</label></th>
<th style="border-left: 1px solid #C1DAD7"> Subject
ID </th>
<th>Title</th>
<th>Units</th>
</tr>
</thead>
<tbody>
<?php
include('../connect.php');
$result = mysql_query("SELECT * FROM tbl_cur_sub where
status='1' ");
while($row = mysql_fetch_array($result))
{
echo '<tr class="record">';
echo ' <td>' . '<input type="checkbox"
name="subject[]" value="'.$rows['code'].'" />' .
'</td> ' ;
echo '<td style="border-left: 1px solid
#C1DAD7">'.$row['code'].'</td>';
echo '<td><div
align="left">'.$row['subject'].'</div></td>';
echo '<td><div
align="left">'.$row['units'].'</div></td>';
echo '</tr>';
}
?>
</tbody>
</table>
<br/>
Course<br>
<select name="course" class="ed">
<?php
include('../connect.php');
$results = mysql_query("SELECT * FROM course");
while($rows = mysql_fetch_array($results))
{
echo '<option>'.$rows['coursecode'].'</option>';
}
?>
</select>
<select name="yearlevel" class="ed">
<?php
include('../connect.php');
$results = mysql_query("SELECT * FROM tbl_yrlevel");
while($rows = mysql_fetch_array($results))
{
echo '<option>'.$rows['yearlevel'].'</option>';
}
?>
</select>
<select name="section" class="ed">
<option>A</option>
<option>B</option>
<option>C</option>
<option>D</option>
</select>
<br>
<br>
<input type="submit" value="Assign" id="button1">
</form>
--The Submission Page -- (setsubject.php)
<?php
include('../connect.php');
//Function to sanitize values received from the form. Prevents SQL injection
function clean($str)
{
$str = @trim($str);
if(get_magic_quotes_gpc())
{
$str = stripslashes($str);
}
return mysql_real_escape_string($str);
}
//Sanitize the POST values
$course = clean($_POST['course']);
$section = clean($_POST['section']);
$yearlevel = clean($_POST['yearlevel']);
$studidnum=$_POST['studidnum'];
$subject=$_POST['subject'];
$N = count($subject);
for($i=0; $i < $N; $i++)
{
mysql_query("INSERT INTO studentsubject (student, subject, section,
course, level) VALUES ('$studidnum',
'$subject[$i]','$section','$course', '$level')");
}
header("location: student.php");
mysql_close($con);
?>
--My Database--
TABLE: studentsubject FIELDS: student, subject, section, course, level
Thanks IN advance for the Help..