<form class="form-inline" action="../includes/login.php" method="post">
                                    <input type="text" name="email" class="form-control mr-2" placeholder="Username/Email">
                                    <input type="password" name="password" class="form-control mr-2" placeholder="Password">
                                    <input type="submit" name="login-submit" class="btn btn-primary mr-2" value="Login">
                                </form>
                                <a href="singup.php" class="btn btn-info mr-2">Signup</a>

if (isset($_POST['login-submit'])) {
    $email = $_POST['email'];
    $password = $_POST['password'];

    if (empty($email) || empty($password)) {
        header("Location: ../public/index.php?error=emptyfields");
        exit();
    } else {
        $conn = mysqli_connect("localhost", "root", "", "expodb");
        $sql = "SELECT * FROM users WHERE username=? OR email=?;";
        $stmt = mysqli_stmt_init($conn);
        if (!mysqli_stmt_prepare($stmt, $sql)) {
            header("Location: ../public/index.php?error=sqlerror");
            exit();
        } else {
            mysqli_stmt_bind_param($stmt, "ss", $email, $email);
            mysqli_stmt_execute($stmt);
            $result = mysqli_stmt_get_result($stmt);
            if ($row = mysqli_fetch_assoc($result)) {
                $passwordCheck = password_verify($password, $row['password']);
                if ($passwordCheck == false) {
                    header("Location: ../public/index.php?error=wrongpassword");
                    exit();
                } elseif ($passwordCheck == true) {
                    session_start();
                }
            } else {
                header("Location: ../public/index.php?error=nouser");
                exit();
            }
        }
    }
} else {
    header("Location: ../public/index.php");
    exit();
}