Displaying menu names from CMS - php

Question

I have been trying to display a menu name from my CMS database that I created myself, I got it displayed perfectly but there is a really weird error, I spent many hours to discover the solution but I couldn't.
The problem is that I want to display the menu name as page H1 in line 50 exactly so whenever you click on the menu name its also displaying as H1 title.
The menu name is displaying correctly, but the sub menu(pages) displaying N instead of the page name, I don't know where is that N is coming from.
NOTE: There is no problem with the database connection or retrieving data.
This is my content page code:
<?php include("includes/header.php"); ?>
<?php require_once 'includes/db_connection.php'; ?>
<?php require_once 'includes/b_functions.php'; ?>
<?php require_once 'includes/cms_constants.php'; ?>
<?php db_connect();?>
<?php
if (isset ( $_GET ['subj'] )) {
$sel_subject = get_subject_by_id ( $_GET ['subj'] );
$sel_page = "NULL";
} elseif (isset ( $_GET ['pages'] )) {
$sel_subject = false;
$sel_page = get_page_by_id ( $_GET ['pages'] );
} else {
$sel_subject = "NULL";
$sel_page = "NULL";
}
?>
<table id="structure">
<tr>
<td id="navigation">
<ul class="subjects">
<?php
$subject_set = get_all_subjects();
while ($subject = mysql_fetch_array($subject_set)) {
echo "<li";
if ($subject["id"] == $sel_subject["id"]) { echo " class=\"selected\""; }
echo "><a href=\"contents.php?subj=" . urlencode($subject["id"]) .
"\">{$subject["menu_name"]}</a></li>";
$page_set = get_pages_for_subject($subject["id"]);
echo "<ul class=\"pages\">";
while ($page = mysql_fetch_array($page_set)) {
echo "<li";
if ($page["id"] == $sel_page["id"]) { echo " class=\"selected\""; }
echo "><a href=\"contents.php?pages=" . urlencode($page["id"]) .
"\">{$page["menu_name"]}</a></li>";
}
echo "</ul>";
}
?>
</ul>
</td>
<td id="page">
<?php if (!is_null($sel_subject)) { // subject selected ?>
<h2><?php echo $sel_subject['menu_name']; ?></h2>
<?php } elseif (!is_null($sel_page)) { // page selected ?>
<h2><?php echo $sel_page['menu_name']; ?></h2>
<div class="page-content">
<?php echo $sel_page['content']; ?>
</div>
<?php } else { // nothing selected ?>
<h2>Select a subject or page to edit</h2>
<?php } ?> </td>
</tr>
</table>
<?php require_once 'includes/footer.php';?>

Answer 1

Your 'N' is coming from the "NULL" string. I believe you meant to set your variables with actual NULL and not a string. Like:
$var = NULL;
As opposed to:
$var = "NULL";
When you access a variable that is set to "NULL" as an array, you will get the 'N' (as the string is treated as an array). For instance;
$var = "NULL";
echo $var[0]; // 'N'
Furthermore, if you test for NULL on a string it will return false (the variable is non-null);
$var = "NULL";
if($var) {
echo "var is: " . $var;
}
else {
echo "var is NULL!";
}
The above should output "var is: NULL".
I say this from experience (I did this when I started coding PHP). However, the root of your problem likely doesn't stop there as your variables should be set in subsequent conditionals. I would go through your while statements, and if statements and ensure your variables are being set appropriately. (var_dump($var) or print_r($var) through suspect blocks).