Catchable fatal error: Object of class mysqli_result could not be converted to string in /hermes/bosnaweb12a/b963/ipg.matjasicborutcom1/TouchSoccer/process.php on line 18

<?php
    include 'dbinfo.php';
    $choice = $_GET['choice'];
    $connect = mysqli_connect($hostname, $username, $password, $database);
    if (mysqli_connect_errno($connect))
    {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }
    switch($choice)
    {
        case "register":

    $username = $_GET['username'];
    $password = $_GET['password'];
    $email = $_GET['email'];
    $reg_ip = $_GET['reg_ip'];


    $query = mysqli_query($connect, "SELECT username FROM Accounts WHERE username = '$username'");


    if($query)
    {
        echo "username already exists";
    }
    else {

        $insert = mysqli_query($connect, "INSERT INTO Accounts (username, password, email,reg_ip, wins, looses, experience) VALUES ('$username', md5('$password'), '$email',  '$reg_ip', '0','0', '0'");
        if($insert) {
                echo "account successfully created";

            }
            else {
                echo "error";
            }

        }

        break;

        case "login":

        $username = $_GET['username'];
        $password = $_GET['password'];

        $user = mysqli_query($connect, "SELECT username FROM Accounts WHERE username = '$username'");

            if($user = $username) {
                $pw = mysqli_query($connect, "SELECT password FROM Accounts WHERE password = md5('$password')");

                if($pw = md5($password)) {
                    echo "login was successful!";
                }
                else {
                    echo "incorrect password";
                }

            }
        else
{
    echo "incorrect username";
        }



        break;


    }

mysqli_close($connect);
?>