package DifferenceOfSquares;
use strict;
use warnings;
use Exporter qw<import>;
our @EXPORT_OK
  = qw<square_of_sum sum_of_squares difference_of_squares>;

sub square_of_sum {
  my ($number) = @_;
  my $sum;
  $sum += $_ foreach (1 .. $number);
  return $sum * $sum;
}

sub sum_of_squares {
  my ($number) = @_;
  my $sum;
  $sum += $_ * $_ foreach (1 .. $number);
  return $sum;
}

sub difference_of_squares {
  my ($number) = @_;
  return square_of_sum($number) - sum_of_squares($number);
}

1;