PHP Undefined index error $_FILES?

Je suis nouveau sur le PHP et je suis en suivant un tutoriel sur YouTube. J'ai tout qui fonctionne dans ce fichier, sauf pour le téléchargement du fichier, toute aide serait appréciée. Voici l'erreur que j'obtiens:

*NOTE: j'ai cherché de nombreuses fois, mais ne pouvait pas trouver undefined index erreur pertinents de la variable $_FILES...

Notice: Undefined index: avatar dans /Applications/xxx sur la ligne 95

Notice: Undefined index: avatar dans /Applications/xxx sur la ligne 96

Notice: Undefined index: avatar dans /Applications/xxx sur la ligne 97

Notice: Undefined index: avatar dans /Applications/xxx sur la ligne 98

Désolé pour ce si c'est une solution simple...

            <?php $title = "Register";?>
<?php require ("styles/top.php") ; ?>           
<?php //de-bugging remove this after script works as desired>
error_reporting(E_ALL);
ini_set("display_errors", 1); 
//end de-bugging//
$form = "<form action='register.php' method='post'>
<table cellspacing='5px'>
<tr>
<td></td>
<td><font color='red'>*</font> are required fields.</td>
</tr>
<tr>
<td>First Name:</td>
<td><input type='text' name='firstname' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Last Name:</td>
<td><input type='text' name='lastname' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Username:</td>
<td><input type='text' name='username' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Email:</td>
<td><input type='text' name='email' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Password:</td>
<td><input type='password' name='password' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Confirm Password:</td>
<td><input type='password' name='repassword' class='textbox'><font color='red'> *</font></td>
</tr>
<tr>
<td>Profile Picture:</td>
<td><input name='avatar' type='file' ></td>
</tr>
<tr>
<td>Profile Message:</td>
<td><textarea name='bio' cols='35' rows='5' class='textbox'></textarea></td>
</tr>
<tr>
<td></td>
<td><input type='submit' name='submitbtn' value='Submit' class='button'></td>
</tr>
</table>
</form>";
if ($_POST['submitbtn']) {
$firstname = strip_tags($_POST['firstname']);
$lastname = strip_tags($_POST['lastname']);
$username = strip_tags($_POST['username']);
$email = strip_tags($_POST['email']);
$class = ($_POST['class']);
$password = strip_tags($_POST['password']);
$repassword = strip_tags($_POST['repassword']);
$bio = strip_tags($_POST['bio']);
//AVATAR UPLOAD
$name = $_FILES['avatar'] ['name'];
$type = $_FILES['avatar'] ['type'];
$size = $_FILES['avatar'] ['size'];
$tmpname = $_FILES['avatar'] ['tmpname'];
$ext = substr($name, strrpos($name, '.'));
if ($firstname && $lastname && $username && $email && $password && $repassword) {
if ($password == $repassword) {
if (strstr($email, "@") && strstr($email, ".") && strlen($email) >= 6) {
require("scripts/connect.php");
$query = mysql_query("SELECT * FROM users WHERE username ='$username'");
$numrows = mysql_num_rows($query);
if ($numrows == 0) {
$query = mysql_query("SELECT * FROM users WHERE email ='$email'");
$numrows = mysql_num_rows($query);
if ($numrows == 0) {
$pass = (md5(md5($password)));
$date = date("F j, Y");
if($name){
move_uploaded_file($tmpname, "avatars/$username.$ext");
$avatar = "$username.$ext";
}
else
$avatar = "default_avatar.png";
$code = substr(md5(rand(111111111111, 99999999999999999)), 2, 25);  
mysql_query("INSERT INTO users VALUES ('', '$firstname', '$lastname', '$username', '$email', '$pass', '$avatar', '$bio', '', '', '$code', '', '$date')"); 
$webmaster = "xxxx";
$subject = "xxxx";
$headers = "From:xxx<$webmaster>";
$message = "xxx";
mail($email, $subject, $message, $headers);
echo "xxx";
}
else
echo "That email is already taken. $form";
}
else
echo "That username is already taken. $form";
}
else
echo "You did not enter a valid email. $form";
}
else
echo "Your passwords did not match. $form";
}
else
echo "You did not fill in all of the required fields. $form";
}
else
echo "$form";
?>
</div>
<?php require ("styles/bottom.php") ; ?>

OriginalL'auteur mais-oui | 2012-06-26