Add role to users.

drupal7-add-role-to-users.php

<?php

$users = array(
  'username1',
  'username2',
);

foreach ($users as $username) {
  $user = user_load_by_name($username);
  $role = user_role_load_by_name("event coordinator");
  $user->roles = $user->roles + array($role->rid => $role->name);
  user_save($user); 
}