zip命令无法在php中工作

I am trying to build application in my website where I can Upload rar files and extract it and store it contents inside a folder named uploads which is in the same folder where the code is .But wnen I run My script I get the following errors. My php version is 5.5.11 Warning: ZipArchive::extractTo(): Invalid or unitialized Zip object in C:\xampp\htdocs\zip ew.php on line 21

Warning: ZipArchive::close(): Invalid or unitialized Zip object in C:\xampp\htdocs\zip ew.php on line 22 my code is as follows

<?php
if(isset($_FILES['zip'])){
    //defined an error erray
    $errors=array();
    $zip = new ZipArchive();
    print_r($_FILES['zip']);
    //taking the extention of the last file (in lower case) of the zip file
    if(strtolower(end(explode('.',$_FILES['zip']['name'])))!=='rar'){
        $errors[]="this is not a zip file";
        echo "file is not opened";
    }
    //if file bigger than 100mb
    if($_FILES['zip']['size']>104857600){
        $errors[]="there is a size limit of 100 mb";
    }
    if($zip->open($_FILES['zip']['tmp_name'])===TRUE){
        echo "file is opened";
        $errors[]="failed to open zip file";
    }
    if(empty($errors)){
        $zip->extractTo('uploads');
        $zip->close();
    }
}
?>
<html>
    <body>
        <form action="" method="POST" enctype="multipart/form-data">
            <div>
                <input type="file" name="zip"/>
                <input type="submit" value="Upload"/>
            </div>
        </form>
    </body>
</html>