$sql = "select login, passwd from Administrator where login='$login' AND passwd='$passwd'";
$req = mysql_query($sql) or die('Erreur SQL Select Admin !<br>'.$sql.'<br>'.mysql_error());
$data = mysql_fetch_assoc($req);
if (empty($data)) // si $rowest vide, c'est que la combinaison user/ password est fausse
{
   echo 'Membre trouvé';
   $_SESSION['login'] = $login;
   $_SESSION['passwd'] = $passwd;

//   echo $col['login'].'<br>';
  // echo $col['passwd'];
}
else
{
  echo "byebye";
}

if (($data['login']==$login) &&  ($data['passwd']==$passwd)) // si $rowest vide, c'est que la combinaison user/ password est fausse
{
   echo 'Membre trouvé';
   $_SESSION['login'] = $login;
   $_SESSION['passwd'] = $passwd;

//   echo $col['login'].'<br>';
  // echo $col['passwd'];
}
else
{
  echo "byebye";
}

mysql_num_rows ==1

donne:
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in c:\program files\easyphp1-7\www\dubaiboy\Admin_Area\VerifAdmin.php on line 70

$sql = "select login, passwd from Administrator where login='$login' AND passwd='$passwd'";
$req = mysql_query($sql) or die('Erreur SQL Select Admin !<br>'.$sql.'<br>'.mysql_error());
if (mysql_num_rows($sql)==1)
{
echo $mysql_num_rows;
   echo 'Membre trouvé';
   $_SESSION['login'] = $login;
   $_SESSION['passwd'] = $passwd;
}
else
{
  echo "byebye";
}

<?
include ('config.php');

if(isset($_POST['date'])) $date = $_POST['date'];
else $date = '';
if(isset($_POST['login'])) $login = $_POST['login'];
else $login = '';
if(isset($_POST['passwd'])) $passwd = (md5($_POST['passwd']));
else $passwd = '';

$date = date("d-m-Y");


if ($login == '')
{
    echo("<font face=verdana size=2>Username field is empty</font>&nbsp;&nbsp;"); //message qui s'affiche si le visiteur n'a pas rempli ce champ
    echo("<a href=\"javascript:history.back()\"> Return </a>");
}
elseif ($passwd == '')
{
   echo("<font face=verdana size=2>Password field is empty</font>&nbsp;&nbsp;"); //message qui s'affiche si le visiteur n'a pas rempli ce champ
    echo("<a href=\"javascript:history.back()\"> Return </a>");
}
elseif (strlen($login) < 4)
{
    echo("<font face=verdana size=2>Username field is less than 4 characters</font>&nbsp;&nbsp;"); //message qui s'affiche si le visiteur n'a pas rempli ce champ
    echo("<a href=\"javascript:history.back()\"> Return </a> <br>");
}
else
{
    $connection = mysql_connect($host, $user, $pass) or die(mysql_error());
    $db = mysql_select_db('database', $connection) or die(mysql_error());
    $sql = "SELECT * FROM administrator WHERE passwd = '". $passwd ."'";
    $result = mysql_query($sql,$connection) or die(mysql_error());
    //get the number of rows in the result set
    $num = mysql_num_rows($result);
    //print a message or redirect elsewhere, based on result
    if ($num == 1 )
    {
                $_SESSION['login'] = $login;
              ?>
<p>Welcome <?php echo($login); ?></p>
<a href="index.php?menu=logout" name="logout">LogOut</a><br>
<a href="index.php?menu=MyAdmin&page=page1">Next</a>
<?php
            }

    else
    {
?>
<p>You're not granted to acceed here : Go out</p>
<a href="index.php" name="retour_accueil" title="Retour à la page d'accueil">Page d'accueil</a>
<?php
    }
    mysql_close();
}
?>

session_start();//demarrage de la session
include ('config.php');

isset($_POST['login'])?$log=addslashes(trim($_POST['login'])):$log='inconnu';
isset($_POST['mdp'])?$mdp=addslashes(trim($_POST['mdp'])):$mdp='inconnu';

$connection = mysql_connect($host, $user, $pass) or die(mysql_error());
$req='select * fron administration where login="'.$log.'" and mdp="'.md5($mdp).'"';//avec achage md5 pour le mdp
$res=mysql_query($req) or die ('Erreur:'.mysql_error()); 
if(mysql_num_row($res)>0)//verif de l'existence de l'utilisateur
{
$_SESSION['log']=$log;
$_SESSION['auth']='oui';
}
else
echo 'non';