checklogin.php

<?php

require_once 'DB_login.php';
require_once 'UTILS.php';

session_start();

$idcheck = $_POST["username"];
$idpassword = $_POST["password"];

//Create connection to database
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT username
        FROM users WHERE username='$idcheck' and password = '$idpassword'";
$result = $conn->query($sql);

//checkErrorReturn is a simple error-reporting and link-offering
//function written in UTILS.php
//Generally, you should put such auxliary functions in separte
//files which can be imported from several scripts
checkErrorReturn
    ($result->num_rows == 0,

     "This username does not exist.",
     "Back to the signin page",
     "index.html");

//$row = $result->fetch_assoc();

//Store the alienname in the session array, to make it available
//to the next page, namely alienPicturesPage
$_SESSION['username'] = $idcheck;

//Instruct client to switch to a new location:
header ("Location: UserHomePage2.php");

?>