form checkbox value php

Question

I have a form created by a while loop in php like this :

<form action='#' method='post'>
<input type='hidden' name='form_valid' id='form_valid'>
<?php
$i=-1;
$result_array = array();
//the while is from a simple mysql query
while( $line = $results->fetch() )
{
  $i++;
  echo"<input type='checkbox' class='checkbox' value='".$line->nid."' id='".$i."'>";
  echo $line->title;
  echo'<br>';
  $result_array[$i] = $line->nid;
}
<input type='submit'>
?>
</form>

Then later on the code I'd like to store the values of the checked checkboxes only in a new array :

if (isset($_REQUEST['form_valid'])) //checking is form is submitted
{
   foreach($result_array as $result)
   {
      if($result == $_REQUEST[$j])  <<<< ERROR
      {
        $final_array[$j] = $result;
      }
   }
 }

Surprisingly, this code does not work at all.
The error message is "Notice : Undefined offset: 0", then offset 1 then 2 etc ...
The line where the message says theres an error is the marked one.

I really have no idea how to do this. Someone ? =)

Answer 1

Don't try to do it this way, this just makes it hard to process, just use a grouping name array: name="checkboxes[<?php echo $i; ?>]" , then on the submission, all values that are checked should simply go to $_POST['checkboxes'] . Here's the idea:

<!-- form -->
<form action="" method="POST">
<?php while($line = $results->fetch()): ?>
    <input type="checkbox" class="checkbox" name="nid[<?php echo $line->nid; ?>]" value="<?php echo $line->nid; ?>" /><?php echo $line->title; ?><br/>
<?php endwhile; ?>
<input type="submit" name="submit" />

PHP that will process the form:

if(isset($_POST['submit'], $_POST['nid'])) {
    $ids = $_POST['nid']; // all the selected ids are in here
    // the rest of stuff that you want to do with it
}