我希望用户可以选择放置文件

Question

我有一个页面（添加帖子），它需要来自用户的输入。但在帖子文件中我不希望它是强制性的。我希望用户可选地插入文件。

怎么做？

    if($file_size > 2097152){
     $missing_input[]='The Post image must be less that 2MB';
    } 

    if($file_size1 > 2097152){
     $missing_input[]='The Post file must be less that 2MB';
    } 

    if($_FILES['image']['error'] == UPLOAD_ERR_NO_FILE){
         $target = "../posts/default.png";
        $check_upload = true;
      } else {
         $target = "../posts/". rand()*78789685 .  $file_name;
        $check_upload = move_uploaded_file($file_tmp,$target);
    }

    if($_FILES['file']['error'] == UPLOAD_ERR_NO_FILE){
         $missing_input[]='The Post file must be selected';
      } else {
         $target1 = "../posts/". rand()*789789789 .  $file_name1;
    }

    $user_id = $_SESSION['student_id'];
    $course_id = $_GET['course_id'];

    if(empty($missing_input) and $check_upload and move_uploaded_file($file_tmp1,$target1))
    {

        $sql="INSERT INTO posts VALUES(NULL,'$title', '$desc', '$target', '$target1', $user_id, $course_id, NOW(), 1)";
        //echo $sql . "<br>";
        $result2= mysqli_query($connection,$sql);
        if($result2) {
            echo "<div class='alert alert-success' style='max-width:460px; margin: 4px auto'>";
                echo 'Your Post Published';
            echo "</div>";
            if($result2) {
                echo '<META HTTP-EQUIV="Refresh" Content="2; URL=index.php?p=posts"/>';
                exit;
            }
        }

    } else {
        foreach($missing_input as $e) {
            echo "<div class='alert alert-danger' style='max-width:500px; margin: 4px auto'>";
                echo $e;
            echo "</div>";
        }
    }
} 
?>