上传多个文件html

I try to combined html and php for multiple file upload on my website. But the result show some code on screen. It happened when I use .html , but it disappeared when I use .php .. what should I do to use .html but the error doesn't happen?

<!DOCTYPE html>
<html>
<body>
<?php
if(isset($_POST['submit'])){
    if(count($_FILES['upload']['name']) > 0){
        
        for($i=0; $i <count($_FILES['upload']['name']); $i++) {
          
            $tmpFilePath = $_FILES['upload']['tmp_name'][$i];

            
            if($tmpFilePath != ""){
            
                //save the filename
                $shortname = $_FILES['upload']['name'][$i];

                //save the url and the file
                $filePath = "upload/" . date('d-m-Y-H-i-s').'-'.$_FILES['upload']['name'][$i];

                
                if(move_uploaded_file($tmpFilePath, $filePath)) {

                    $files[] = $shortname;
                    

                }
              }
        }
    }

   
    echo "<h1>Uploaded:</h1>";
    if(is_array($files)){
        echo "<ul>";
        foreach($files as $file){
            echo "<li>$file</li>";
        }
        echo "</ul>";
    }
}
?>

<form action="" enctype="multipart/form-data" method="post">

    <div>
        <label for='upload'>Add Attachments:</label>
        <input id='upload' name="upload[]" type="file" multiple="multiple" />
    </div>

    <p><input type="submit" name="submit" value="Submit"></p>

</form>
</body>
</html>

What should I edit? Thanks.

</div>

first: Please run your script on server side using wamp or similar servers

second: I guess the following edit t your code

count($_FILES) not count($_FILES['file']['name'])

third: also, have to check the files are empty or not for the first time