echo ("<tr bgcolor='B0C4DE'>");
$value=$row['idbook_code'];
$author=$row['b_author'];
$book=$row['b_name'];
echo ('ISBN : '.$row['idbook_code'].'<br/>');
echo ('Title : '.$row['b_name'].'<br/>');
echo ('Author : '.$row['b_author'].'<br/>');
echo ('Books Available : '.$row['b_avail'].'<br/>');
if($row['b_avail']>0)
{
if (!$_SESSION["valid_user"])
{
// User not logged in, redirect to login page
echo("Available".'<br/>');
}else
{
echo("<input type='hidden' name='idbook' value='$value'>");
echo("<input type='hidden' name='author' value='$author'>");
echo("<input type='hidden' name='book' value='$book'>");
?>
<input type='submit' name='submitbutton' value='Add to Cart' onsubmit='submitPressed()' ><br/>
<?php
}
}else
echo("No stock of book".'<br/>');
echo("</tr>".'<br/>');
echo("<tr>");echo("==============");echo("</tr>".'<br/>');
?>
how can i disable a button is clicked