function userExists($pdow, $login)
{
$userQuery = "SELECT * FROM login u WHERE login=:user;";
$stmt = $pdow->prepare($userQuery);
$stmt->execute(array(':user' => $login));
return !!$stmt->fetch(PDO::FETCH_ASSOC);
}

$login = 'user';
$exists = userExists($pdow, $login);
if('$login')
$user= var_dump((bool) 'Exists');
{
echo "Login exsists!";
}

if($login)
            // this line doesnt make any sense!
            // $user= var_dump((bool) 'Exists');
            // so this is not a valid if clause
       {
           echo "Login exsists!";
       }`

$servername = '';
    $dbname = '';
    $username = '';
    $password = '';
    $dbh = new PDO("mysql:host={$servername};dbname={$dbname}", $username, $password);


function user_exists($dbh, $login) {
    $Q = $dbh->prepare("SELECT * FROM login WHERE login = :Login");
    $Q->bindParam(':login', $Login);
    $Q->execute();

    if ($Q->rowCount() != 0) {
        //User exist:
        return $Q->fetch(PDO::FETCH_ASSOC);
    } else {
        //User doesn't exist.
        return false;
    }
}

//Lets try:
$check = user_exists($dbh, 'email@example.com');
if ($check) {
    echo 'User: ' . $check['login'] . ' was found int he database.';
} else {
    echo 'The user was NOT found.';
}