sub sum {
    my $list = shift;
    my $sum = 0;
    while (my $i = shift @$list) {
      $sum += $i;
    }
    return $sum;
}
my @values = qw(1 2 3 4 5 6 7);
print sum(\@values), " ; '@values'\n";

##</code><code>##

sub add_two {
    my $arrayref = shift;
    $_ += 2 foreach @$arrayref;
    return 1;
}
my @values = qw( 1 2 3 4 5 6 7 );
print add_two(\@values), " ; '@values'\n";

##</code><code>##

sub sanitize_strings {
   my $arrayref = shift;
   s/[^a-zA-Z0-9_\-]/_/g foreach @$arrayref;
   return 1;
}
my @strings = qw( abc 123 a&21 j**!k );
print sanitize_strings(\@strings), " ; '@strings'\n";