move_uploaded_file未定义索引文件[重复]

move_uploaded_file undefined index file error, Why am I getting this error? how to fix this?

<?php
if (!file_exists("upload")) {
    mkdir("upload");
}

if (isset($_POST["regform"])) {
    if (!empty($_FILES["file"]["tmp_name"])) {
        $fileName = explode(".", $_FILES["file"]["name"]);
        if ($fileName[1] == "csv") {
            move_uploaded_file($_FILES["files"]["tmp_name"], "upload/" . $_FILES["file"]["name"]);
            echo "Stored in : " . "upload/" . $_FILES["file"]["name"];
        } else {
            echo " You must choose a csv file to upload!!";
        }
    } else {
        echo "You must choose a file!!";
    }
    echo "";
}

?>

</div>

You have a spelling error

Here
move_uploaded_file($_FILES["files"]["tmp_name"], "upload/" .$_FILES["file"]["name"]);

You have an extra 's' in the first $_FILES['fileS']

it should be
move_uploaded_file($_FILES["file"]["tmp_name"], "upload/" .$_FILES["file"]["name"]);