my @foo = (2, 4, 8);
foreach my $num (@foo) {
    $num *= 2;
}
$, = ",";print @foo;print "\n";

##</code><code>##

my @foo = (2, 4, 8);
foreach my $num (@foo) {
    &double($num);
}
$, = ",";print @foo;print "\n";

sub double {
    $_[0] =  2*$_[0];  
    return $_[0];
}

##</code><code>##

sub double {
    my $num = $_[0];
    $num =  2*$num;  
    return $num;
}