Erreur variable et offset

bonjour a tous,

Je commence un petit developpement en rapport avec l'API Goole Books.
Apres de multiples recherche il me reste deux erreurs que je n'arrive pas à résoudre :

La 1ere : Notice: Undefined variable: httpClient in C:\Fichiers\Developpement\Sites Web\Local\galmiore.free.fr\listing3.php on line 37
Elle apparait non pas au load de la page mais apres que j'ai cliqué sur mon bouton de recherche
La ligne de mon code (que je vais coller plus bas) qui corresponds a cette erreur est

Code:

$books = new Zend_Gdata_Books($httpClient);

la 2nd :Notice: Undefined offset: 0 in C:\Fichiers\Developpement\Sites Web\Local\galmiore.free.fr\listing3.php on line 165
elle apparait presque a toutes les lignes.
La ligne de mon code (que je vais coller plus bas) qui corresponds a cette erreur est

Code:

$book->subject = is_object($arr[0]) ?

et voici la totalité du code que j'ai construit en puisant des ressources à droite et à gauche :

Code:

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<?php
 
// start a new session 
session_start();
 
if (isset($_POST['submit'])) {
 
// load Zend Gdata libraries
require_once 'Zend/Loader.php';
Zend_Loader::loadClass('Zend_Gdata_Books');
Zend_Loader::loadClass('Zend_Gdata_Books_VolumeQuery');
Zend_Loader::loadClass('Zend_Gdata_AuthSub');
 
function getAuthSubRequestUrl()
{
    $next = 'http://www.example.com/welcome.php';
    $scope = 'http://www.google.com/books/feeds';
    $secure = false;
    $session = true;
    return Zend_Gdata_AuthSub::getAuthSubTokenUri($next, $scope, $secure, $session);
}
 
function getAuthSubHttpClient()
{
    if (!isset($_SESSION['sessionToken']) && !isset($_GET['token']) ){
        echo '<a href="' . getAuthSubRequestUrl() . '">Login!</a>';
        return;
    } else if (!isset($_SESSION['sessionToken']) && isset($_GET['token'])) {
      $_SESSION['sessionToken'] = Zend_Gdata_AuthSub::getAuthSubSessionToken($_GET['token']);
    }
 
    $httpClient = Zend_Gdata_AuthSub::getHttpClient($_SESSION['sessionToken']);
    return $httpClient;
}
 
 //$books = new Zend_Gdata_Books($httpClient, $applicationId, $clientId);
$books = new Zend_Gdata_Books($httpClient);
 
try {
 // prepare and execute search query
    $query = new Zend_Gdata_Books_VolumeQuery;
    $queryStr = '';
    if (!empty($_POST['title'])) {
      $queryStr .= '+intitle:'.urlencode($_POST['title']);
    }
    if (!empty($_POST['author'])) {
      $queryStr .= '+inauthor:'.urlencode($_POST['author']);
    }    
    $query->setQuery($queryStr);
    $query->setMinViewability($_POST['v']);
    $query->setMaxResults(20);
 
    $feed = $books->getVolumeFeed($query);  
  } catch (Exception $e) {
    die('ERROR:' . $e->getMessage());  
  }
}  
?>
<!DOCTYPE html 
  PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr" lang="fr">
  <head>
    <title>Searching for book titles</title>
    <style>
    .entry {
      height: 120px;
      border-bottom: dashed silver 2px;
      padding-top: 10px;
    }
 
    .thumbnail {
      float: left;  
      border: solid black 2px;
      padding: 2px;
      margin-right: 10px;
    }
 
    .desc {
      font-style: italic;  
    }
 
    .small {
      font-size: smaller;  
    }    
    </style>    
  </head>
  <body>
 
    <h2>Search</h2>
    <form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    Title: 
    <input type="text" name="title" value="<?php echo isset($_POST['title']) ? 
     $_POST['title'] : ''; ?>" />
 
    Author: 
    <input type="text" name="author" value="<?php echo isset($_POST['author']) ? 
     $_POST['author'] : ''; ?>" />
 
    Viewability:
    <select name="v">
      <option value="none">Any</option>
      <option value="partial_view">Partial</option>
      <option value="full_view">Full</option>
    </select>    
 
    <input type="submit" name="submit" value="Go" />
    </form>
 
    <?php if (isset($feed)): ?>
      <h2>Search results for '<?php echo $query->getQuery(); ?>'
      </h2>
      <div>
      <?php echo $feed->totalResults; ?> result(s) found.
      </div>
 
      <div id="results">
      <?php $x = 1; ?>
      <?php foreach ($feed as $entry): ?>
 
        <?php    
        //print_r($entry);   
        $book = new stdClass;
 
        // get title
        if (is_array($entry->getTitles())) {
          foreach ($entry->getTitles() as $title) {
            $book->titles[] = $title->getText(); 
          }
        }
 
        // get authors
        if (is_array($entry->getCreators())) {
          foreach ($entry->getCreators() as $creator) {
            $book->authors[] = $creator->getText(); 
          }
        }
 
        // get publishers
        if (is_array($entry->getPublishers())) {
          foreach ($entry->getPublishers() as $publisher) {
            $book->publishers[] = $publisher->getText(); 
          }
        }
 
        // get publication date
        if (is_array($entry->getDates())) {
          $arr = $entry->getDates();
          $book->pubdate = (is_object($arr[0])) ? 
           $arr[0]->getText() : 'Unspecified'; 
        }
 
        // get ISBN numbers
        if (is_array($entry->getIdentifiers())) {
          foreach ($entry->getIdentifiers() as $id) {
            if (preg_match('/ISBN/', $id->getText())) {
              $book->isbn[] = $id->getText(); 
            }  
          }
        }
 
        // get first subject
        if (is_array($entry->getSubjects())) {
          $arr = $entry->getSubjects();
          $book->subject = is_object($arr[0]) ? 
           $arr[0]->getText() : 'Unspecified'; 
        }
 
        // get first description
        if (is_array($entry->getDescriptions())) {
          $arr = $entry->getDescriptions();
          $book->desc = is_object($arr[0]) ? 
           $arr[0]->getText() : 'No description available'; 
        }            
        ?>
 
        <div class="entry">
          <div class="thumbnail">
            <img src="<?php echo ($entry->getThumbnailLink()) ? 
             $entry->getThumbnailLink()->getHref() : ''; ?>" />      
          </div>
          <div class="data">
          <?php echo $x; ?>. <?php echo ucwords(@implode(': ', 
           $book->titles)); ?><br/>
          <?php echo @implode(', ', $book->authors); ?> |
          <?php echo @implode(', ', $book->publishers); ?> |
          <?php echo $book->subject; ?> |
          <?php echo date('d M Y', strtotime($book->pubdate)); ?> <br/>
          <span class="desc"><?php echo $book->desc; ?></span> 
          <br/>
          <span class="small"><?php echo @implode(', ', $book->isbn); ?> |       
            <a href="<?php echo $entry->getInfoLink()->getHref(); ?>">
            More information</a>   
          </span>
          </div>
        </div>      
        <?php $x++; ?>
      <?php endforeach; ?>
    <?php endif; ?>
 
  </body>
</html>

Quelqu'un pourrait il m'expliquer afin que je comprenne et ne plus recommetre ces erreurs?

Merci d'avance a celui et ceux qui auront pris le tps de lire ceci et d'y repondre.

Anax