my %Q = CGI::Vars();
...
$id_cust = AddCusomer($Q{login}, $Q{pass}, $Q{name}, $Q{email}, ...)
    if $Q{pass} eq $Q{confirmpass};
...
sub AddCustomer {
    my ($login, $pass, $name, $email, ...) = @_;
    $dbh->do("INSERT INTO Customer SET login=?, pass=?, name=?,
        email=?, ...", undef, $login, $pass, $name, $email, ...)
        or return;
    $dbh->selectrow_array("SELECT LAST_INSERT_ID()");
}