Memberhentikan skrip php

gimana caranya supaya skrip php yang dibawahnya tidak dijalankan jika ketemu $aktiferror = true / $loginerror = true

if(isset($_POST['login'])){
	$username = $_POST['username'];
	$password = $_POST['password'];

	 $query =  mysqli_query($conn, "SELECT * FROM users WHERE username = '$username'");

	 if(mysqli_num_rows($query) === 1){
		 $row = mysqli_fetch_assoc($query);
	 	if(password_verify($password, $row["password"])){
	 		if($row['aktif'] === 'Y'){
		 		$_SESSION['login'] = true;
		 		$_SESSION['id_user'] = $row['id_user'];
				$_SESSION['nama'] = $row['nama'];
				$_SESSION['username'] = $row['username'];
				$_SESSION['avatar'] = $row['avatar'];
				$_SESSION['deskripsi'] = $row['deskripsi'];
			 	header("Location: index.php");
			 	exit;
			 	}

			 	$aktiferror = true;
	 		}

	 }

	 $loginerror = true;
}