sub average {
    if (@_) {
        my $sum;
        for (@_) {
            $sum += $_;
        }
        return $sum/@_;
    } else {
        return undef;
    }
}

##</code><code>##

sub sum { my $sum; $sum += $_ for @_; $sum }
sub avg { @_ ? sum(@_)/@_ : undef }