REGISTRAZIONE
.......
$usr= $_POST['username'];
$pass = MD5($_POST['password']);

$c=$mysql->query("INSERT INTO utenti (`user`,`pass`) VALUES('$usr','$pass')");
........


LOGIN:
.........
if(mysqli_connect_errno())
  printf("errore: ", mysqli_connect_errno());

$user = $_POST['username'];
$pass = MD5($_POST['p']);
echo $pass;

$result= $mysql->query("SELECT COUNT(`user`) FROM utenti WHERE user LIKE \"'$user'\" AND password LIKE \"'$pass'\"");
..........
......