login.php

<?php

session_start(); //starting session
$error = ''; //variable to store error message

if (isset($_POST['submit'])) {

  if (empty($_POST['username']) || empty($_POST['password'])) {
    $error = "Nick i Hasło nie mogą być puste!"; //error empty pwd and nick
  }
  else {
    $username = $_POST['username']; //define username
    $password = $_POST['password']; //define password

    //connect with database
    $conn = mysqli_connect("localhost", "00194748_otako", "090909B1", "00194748_otako");

    //matching password and username with database
    $query = "SELECT username, password FROM login WHERE username=? AND password=? LIMIT 1";

    //security
    $stmt = $conn -> prepare($query);
    $stmt -> bind_param("ss", $username, $password);
    $stmt -> execute();
    $stmt -> bind_result($username, $password);
    $stmt -> store_result();

    if ($stmt -> fetch()) {
      $_SESSION['login_user'] = $username; //session initializing
      header("location: profile.php"); //rediecting to profile page
    }
    else {
      $error = "Nick lub/i Hasło jest/są niepoprawne/niepoprawny";
    }
    mysqli_close($conn); //closing connection
  }
}

?>