使用mysqli编写的mysql数据库获取名字和姓氏？

This is a small problem but I have been spending hours trying to figure out why it doesn't work.

I am trying to get firstname or lastname from the mysql database using the following code:

<?php
 include "config/connect.php";

 $manager = 'myemail@yahoo.co.uk';

    $stmt = mysqli_prepare(
    $db_conx,
    "SELECT  lastname
     FROM members
     WHERE email = ?
     AND lastname = ?");
//after validation, of course
mysqli_stmt_bind_param($stmt, "ss", $manager, $lastname);
mysqli_stmt_execute($stmt);
print $lastname;
if (mysqli_affected_rows($db_conx))
{
    mysqli_stmt_close($stmt);//<-- CLEAN UP AFTER YOURSELF!
    $id = mysqli_insert_id($db_conx);


}
?>

for some strange reason it just doesn't print the lastname or the lastname at all. but if I print manager, it prints it out properly.

what am I doing wrong?

P.S. i know the email, firstname and lastname all exist in the database.

EDIT:

 include "config/connect.php";

 $manager = 'MYEMAIL@yahoo.co.uk';


$stmt = $db_conx->prepare("SELECT  email, firstname
     FROM members
     WHERE email = ?
       AND firstname = ?");
    $stmt->bind_param('ss', $manager, $firstname);
    $stmt->execute();
    $stmt->bind_result($manager, $firstname);
    $stmt->store_result();
    if($stmt->num_rows == 1)  //To check if the row exists
        {
            while($stmt->fetch()) //fetching the contents of the row

              { 
         $firstname = $firstname;
         $manager = $manager;


              }
        }
        $stmt->close();

i didn't understand ,what your trying to do,

If you want to get FIRSTNAME AND LASTNAME

$stmt = mysqli_prepare($db_conx,"SELECT  firstname,lastname FROM members WHERE email = ?");
$stmt->bind_param('s', $manager);

 $stmt->execute();
$stmt->bind_result($fname, $lname);

/* fetch values */

while ($stmt->fetch()) {
    printf("%s %s
", $fname, $lname);
}