PHP unitialized string offset: 0 - php

Question

I decided to give PHP a try, and then bought lynda.com's essential training tutorial.
The problem is, that I get this error:
( ! ) Notice: Uninitialized string offset: 0 in
C:\wamp\www\widget_corp\includes\functions.php on line 147.
when trying to compare two values.
Can anyone help me ? :)
error in navigation function:
if($page["id"] == $selectedPage['id']){
Class content.php below:
<?php require_once("includes/connection.php"); ?>
<?php require_once("includes/functions.php");?>
<?php findSelectedPage(); ?>
<?php include("includes/header.php");?>
<table id="structure">
<tr>
<td id="navigation">
<?php echo navigation($selSubject, $selectedPage);?>
<br/>
+ Add a new subject
</td>
<td id="page">
<?php echo checkSubjOrPage();?>
<br/>
<div id="footer">Copyright 2007, Widget Corp</div>
</td>
</tr>
</table>
<?php require("includes/footer.php"); ?>
class function.php below:
<?php
//This file is the place to store all basic functions.
//NB!
//function to prevent problems with submitting values, that contains
//chars such as: "", '' etc., into the database.
function mysql_prep($value){
$magic_quotes_active = get_magic_quotes_gpc;
//i.e. php>= v4.3.0
$new_enough_php = function_exists("mysql_real_escape_string");
if($new_enough_php){
//undo any magic quotes effects so mysql_real_escape_string can do the work
if($magic_quotes_active){
$value = stripslashes($value);
}
$value = mysql_real_escape_string($value);
} else { // before PHP v4.3.0
//if magic quotes aren't already on then add slashed manually
if(!$magic_quotes_active){
$value = addslashes($value);
}
}
return $value;
}
function confirm_query($result_set){
if(!$result_set){
die("Database connection failed: " . mysql_error());
}
}
function getAllSubjects(){
global $connection;
$query = "SELECT *
FROM subjects
ORDER BY position ASC";
$subject_set = mysql_query($query, $connection);
confirm_query($subject_set);
return $subject_set;
}
function getPagesForSubject($subject_id){
global $connection;
$query = "SELECT *
FROM pages
WHERE subject_id = {$subject_id}
ORDER BY position ASC";
$page_set = mysql_query($query, $connection);
confirm_query($page_set);
return $page_set;
}
function get_subject_by_id($subject_id){
global $connection;
$query = "SELECT * ";
$query .= "FROM subjects ";
$query .= "WHERE id=" . $subject_id . " ";
$query .= "LIMIT 1";
$result_set = mysql_query($query, $connection);
confirm_query($result_set);
//REMEMBER:
//if no rows are returned, fetch_array will return false.
if($subject = mysql_fetch_array($result_set)){
return $subject;
} else {
return NULL;
}
}
function get_page_by_id($page_id){
global $connection;
$query = "SELECT * ";
$query .= "FROM pages ";
$query .= "WHERE id=" . $page_id . " ";
$query .= "LIMIT 1";
$result_set = mysql_query($query, $connection);
confirm_query($result_set);
//REMEMBER:
//if no rows are returned, fetch_array will return false.
if($page = mysql_fetch_array($result_set)){
return $page;
} else {
return NULL;
}
}
function checkSubjOrPage(){
global $selSubject;
global $selectedPage;
if(!is_null($selSubject)){
return "<h2>" . $selSubject['menu_name'] . "</h2>";
} else if(!is_null($selectedPage)){
return "<h2>" . $selectedPage['menu_name'] . "</h2>" . "<div>" . $selectedPage['content'] . "</div>";
} else {
return "<h2>" . "Select a subject or page to edit!" . "</h2>";
}
}
function findSelectedPage(){
global $selSubject;
global $selectedPage;
if(isset($_GET['subj'])){
$selSubject = get_subject_by_id($_GET['subj']);
$selectedPage = "";
} else if(isset($_GET['page'])){
$selSubject = NULL;
$selectedPage = get_page_by_id($_GET['page']);
} else {
$selectedPage = NULL;
$selSubject = NULL;
}
}
function navigation($selSubject, $selectedPage){
$output = "<ul class=\"subjects\">";
//3. Perform our database query
$subject_set = getAllSubjects();
while($subject = mysql_fetch_array($subject_set)){
$output .= "<li";
if($subject["id"] == $selSubject['id']){
$output .= " class=\"selected\"";
}
$output .= "><a href=\"content.php?subj=" . urlencode($subject["id"]) .
"\">{$subject["menu_name"]}</a></li>";
$page_set = getPagesForSubject($subject["id"]);
$output .= "<ul class=\"pages\">";
while($page = mysql_fetch_array($page_set)){
$output .= "<li";
if($page["id"] == $selectedPage['id']){
$output .= " class=\"selected\"";
}
$output .= "><a href=\"content.php?page=" . urlencode($page{"id"}) .
"\">{$page["menu_name"]}</a></li>";
}
$output .= "</ul>";
}
$output .= "</ul>";
return $output;
}
function getPositions(){
$subject_set = getAllSubjects();
$subject_counts = mysql_num_rows($subject_set);
$output = "<select name=\"position\">";
//$subject_counts + 1 b/c we are adding a subject.
for($count = 1; $count <= $subject_counts +1; $count++){
$output .= "<option value=\"{$count}\">{$count}</option>";
}
return $output . " </select>";
}
?>

Answer 1

here you override $selectedPage to a string or set it to null
function findSelectedPage(){
global $selSubject;
global $selectedPage;
if(isset($_GET['subj'])){
$selSubject = get_subject_by_id($_GET['subj']);
$selectedPage = "";
} else if(isset($_GET['page'])){
$selSubject = NULL;
$selectedPage = get_page_by_id($_GET['page']);
} else {
$selectedPage = NULL;
$selSubject = NULL;
}
}
And here it should be an array:
if($page["id"] == $selectedPage['id']){
function findSelectedPage(){
global $selSubject;
global $selectedPage;
if(isset($_GET['subj'])){
$selSubject = get_subject_by_id($_GET['subj']);
$selectedPage = NULL;
} else if(isset($_GET['page'])){
$selSubject = NULL;
$selectedPage = get_page_by_id($_GET['page']);
} else {
$selectedPage = NULL;
$selSubject = NULL;
}
}
function navigation($selSubject, $selectedPage){
$output = "<ul class=\"subjects\">";
//3. Perform our database query
$subject_set = getAllSubjects();
while($subject = mysql_fetch_array($subject_set)){
$output .= "<li";
if(isset($selSubject['id']) && $subject["id"] == $selSubject['id']){
$output .= " class=\"selected\"";
}
$output .= "><a href=\"content.php?subj=" . urlencode($subject["id"]) .
"\">{$subject["menu_name"]}</a></li>";
$page_set = getPagesForSubject($subject["id"]);
$output .= "<ul class=\"pages\">";
while($page = mysql_fetch_array($page_set)){
$output .= "<li";
if(isset($selectedPage['id']) && $page["id"] == $selectedPage['id']){
$output .= " class=\"selected\"";
}
$output .= "><a href=\"content.php?page=" . urlencode($page{"id"}) .
"\">{$page["menu_name"]}</a></li>";
}
$output .= "</ul>";
}
$output .= "</ul>";
return $output;
}