file - PHP Undefined index error $_FILES?

I am new to PHP and am following a tutorial on YouTube. I have everything working in this file, except for the file uploading, any help would be appreciated. Here is the error i am getting:

*NOTE: I have looked for this many times, but could not find undefined index error relevant to $_FILES...

Notice: Undefined index: avatar in /Applications/xxx on line 95

Notice: Undefined index: avatar in /Applications/xxx on line 96

Notice: Undefined index: avatar in /Applications/xxx on line 97

Notice: Undefined index: avatar in /Applications/xxx on line 98

Sorry for this if it is a simple fix...

            
                   

        
        error_reporting(E_ALL);
         ini_set("display_errors", 1); 
        //end de-bugging//

        $form = "

        













































            
                
                
* are required fields.
            
            
                
First Name:
                
 *
            
            
                
Last Name:
                
 *
            
            
                
Username:
                
 *
            
            
                
Email:
                
 *
            
            
                
Password:
                
 *
            
            
                
Confirm Password:
                
 *
            
            
                
Profile Picture:
                
            
            
                
Profile Message:
                
            
            
                
                
            
        
        
";



        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";


            ?>