dynamic checkbox value access in another file in PHP - php

Question

i am facing problem i am developing school system in php.
i want use checkbox dynamic for attendance but checkbox value i cant use in another file please help me
first file attendacne.php
<form name="abc" method="post" action="attendance-con.php">
<p>Date:
<input name="dat" type="text" class="tcal"/>
<input name="Save" type="submit" style="float:right 20ox;" value="Save Attendace" />
<input name="class_id" type="hidden" value="<?php echo $_REQUEST['class_id']; ?> " />
<?php
$a=0;
$qry=("SELECT DISTINCT
s.rollnum as rollnum,
s.std_name as name
FROM student s WHERE s.std_class=".$_REQUEST['class_id']."");
$result=mysql_query($qry);
while($row=mysql_fetch_array($result))
{
?>
<table width="100%" border="1" align="center" cellpadding="4" cellspacing="4" style="text-align:left;" id="stname">
<?php
if($a==0)
{ ?>
<tr>
<th width="117" height="39" bgcolor="#FFE1CC">Student RollNo</th>
<th bgcolor="#FFE1CC">Student Name</th>
<th width="100" bgcolor="#ECFAFF">Present</th>
</tr>
<?php
}?>
<?php
if($a==1)
{ ?>
<tr>
<th width="117" height="-5" bgcolor="#FFE1CC"></th>
<th bgcolor="#FFE1CC"></th>
<th width="100" bgcolor="#ECFAFF"></th>
</tr>
<?php
}
?>
<?php $a=1; ?>
<input type="hidden" name="rollnum[]" value="<?php echo $row['rollnum'];?>"/><tr>
<td>
<?php echo $row['rollnum'];?>
</td>
<td>
<?php echo $row['name'];?>
</td>
<td>
<input type="checkbox" name="stid[]" value="1">
</td>
</tr>
<?php }?>
</table>
</form>
second file attendance-con.php
<?php
include_once("include/config.php");
$i=0;
$Dat=$_POST['dat'];
$cid=$_POST['class_id'];
$sid=$_POST['stid'];
foreach($_POST['rollnum'] as $x)
{
if($sid[$i]=='1')
{
$query=mysql_query("INSERT INTO attendance (sid,cid,Date,status)
values('$x','$cid','$Dat','1')");
}
if($sid[$i]!='1')
{
$query=mysql_query("INSERT INTO attendance (sid,cid,Date,status)
values('$x','$cid','$Dat','0')");
}
$i=$i+1;
}
?>

Answer 1

<input type="checkbox" name="stid" value="1">
not
<input type="checkbox" name="stid[]" value="1">