antoine_cherfane help php

<?php

$host = "localhost";
$user = "root";
$pass = "";
$data = "Skyhigh";

$con = new mysqli($host, $user, $pass, $data);

if($con->connect_errno)
{
    printf("Connect failed: %s\n", $con->connect_error);
}

$action = $_GET['action'];

$username = $con->real_escape_string($_GET['username']);
$password = $con->real_escape_string($_GET['password']);


//Enctrypt passwords START
$encpassword = hash('sha256', $password);
//Encrypt passwords END


if(!$action)
{
    echo "Please enter an action.";
}
else
{
    if($action == "register")
    {


        $result = mysqli_query("SELECT * FROM users WHERE username = " . $username);
if(mysql_num_rows($result) == 0) {
     // row not found, do stuff...


if($query = $con->query("INSERT INTO users (id,username,password) VALUES (null, '$username','$password')"))
        {
            echo "1";
        }
        else
        {
            echo "0";
        }
    }
else
{
echo "0";
}}


    else if($action == "login")
    {
        $query = $con->query("SELECT * FROM users WHERE username = '$username' and password = '$encpassword'");
        $cnt = $query->num_rows;

        if($cnt > 0)
        {
            echo "1";
        }
        else
        {
            echo "0";
        }
    }
}

?>