Question

<?php

$current_subject = $_GET['subject_id'];
$current_content = $_GET['note_id'];

echo "<form method=\"post\" action=mainpage.php?subject_id=".$current_subject."&note_id=".$current_content.">";

?> 
  <input type='text' name='list_item' value=''>
  <input type='submit' name="new_item" value="New Item">   
</form>

The problem is that when one of the GET variables is two words the link doesn’t write it that way. So for example if $current_subject="Advanced Chemistry" and $current_content="Valence Electrons" the link will come out as:

<form method=​"post" action=​"mainpage.php?subject_id=Advanced" chemistry&note_id=​"Valence" electrons>​

Answer 1

You need to urlencode() the variables like so:

<?php

$current_subject = $_GET['subject_id'];
$current_content = $_GET['note_id'];

$subject = urlencode($current_subject);
$content = urlencode($current_content);

$action = "mainpage.php?subject_id=" . $subject . "&note_id=" . $content;

?>

<form method="post" action="<?php echo $action; ?>">
  <input type="text" name="list_item" value="">
  <input type="submit" name="new_item" value="New Item">   
</form>

Also, you should get in the habit of validating that data. You probably want to check that they are integers.