saving simple checkbox boolean php

Something basic but I don’t see why it doesn’t work I want to save the state of a checkbox in a database, type Boolean, if checked 1 else 0 here is my code:

<input type="checkbox" name="stok"  value="1"
  <?php if(isset($_POST['stok'])) echo "checked='checked'"; ?>
/>
<?php
    if (isset($_POST['stok']) && !empty($_POST['stok']) && $_POST['stok'] === 'on')               
        $stok = 1;  
    else 
        $stok = 0;      

    mysql_query ("update tab set etat_vendu=$stok where id=$big");
?>  

//this is my var $stok=$row['stok'];   

Answer

This will work:

if(isset($_POST['stok'])){
    //$stok is checked and value = 1
    $stok = $_POST['stok'];
}
else{
    //$stok is nog checked and value=0
    $stok=0;
}