my $params = &CheckParams($cgi, a => 20, b => 40, c => 50);

sub CheckParams {
  my ($cgi, %standardParameters) = @_;

  my $params = $cgi->Vars();
  foreach (keys %standardParameters) {
    unless (defined $params->{$_}) {
      $params->{$_} = defined($standardParameters{$_}) ? $standardParameters{$_} : '';
    } # unless
  } # foreach
  return $params;
}