如果输入为空，如何阻止一行代码运行

I have this line of code, and i would like it to not run when "beg_img" is empty, i got the code from w3schools and changed minior things, im pretty new to this, but i guess i have to use some kind og if/else isset?

<?php
$target_dir = "../../img/images/";
$target_file = $target_dir . basename($_FILES["beg_img"]["name"]);
$uploadOk = 1;
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["beg_img"]["tmp_name"]);
    if($check !== false) {
        echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "File is not an image.";
        $uploadOk = 0;
    }
}

// Check if file already exists
if (file_exists($target_file)) {
    echo "Sorry, file already exists.";
    $uploadOk = 0;
}
// Check file size
if ($_FILES["beg_img"]["size"] > 500000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}
// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg") {
    echo "Sorry, only JPG, JPEG & PNG files are allowed.";
    $uploadOk = 0;
}
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    if (move_uploaded_file($_FILES["beg_img"]["tmp_name"], $target_file)) {
        echo "The file ". basename( $_FILES["beg_img"]["name"]). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}

$beg_i_img = basename($_FILES["beg_img"]["name"]);

?>

Or you can try this at the beggining of your script:

// If no file was uploaded
if($_FILES['beg_img']['error'] == 4){
    return;
}

And it's better to validate some things like the one you want at the beggining of your script than wrap all your code with an if, because one more wrap, then another and another...if we can avoid it, the code will be better :)

You should check return and maybe continue, will help you in your scritps :)

Surround your entire code with an "if":

if (($_FILES["beg_img"]) != NULL) && (!empty($_FILES["beg_img"])) { 
   //yourcode 
}

You can also check directly if the $_FILES["beg_img"] not exists with

if (isset($_FILES["beg_img"])){
   //yourcode
}

You can try this:

if (isset($_FILES["beg_img"])){
}

I use this on my scripts and works fine

Return false when $_FILES["beg_img"] is empty, like:

if (empty($_FILES["beg_img"]))
{
    return false;
}