Be careful with types. PHP switches automatically between strings and numbers, but LDAP doesn't, and PHP will send whatever is most convenient for PHP, not LDAP, unless you specify a type.
If you inadvertently send a number as a string, you will get an error: "ldap_add(): Add: Invalid syntax in [filename] on line LINENUM."
Observe this example which makes an array to send to LDAP to create a POSIX group. Note that $new_groupid, which is technically a string, must be typecast with (int).
$new_ldap_group['cn'] = $groupname;
$new_ldap_group['objectclass'][0] = 'posixgroup';
$new_ldap_group['objectclass'][1] = 'top';
$new_ldap_group['gidnumber'] = (int) $new_groupid;
