difference_of_squares.rb

require 'pry'

class Squares

  def initialize(num)
    @num = num
  end

  def square_of_sum
    square_of_sum = 0
    (1..@num).each do |i|
      square_of_sum += i
    end
    @square_of_sum = square_of_sum**2
  end

  def sum_of_squares
    sum_of_squares = 0
    (1..@num).each do |i|
      sum_of_squares += i**2
    end
    @sum_of_squares = sum_of_squares
  end

  def difference
    difference = @square_of_sum - @sum_of_squares
    #? what do i do here to call second & third function first before this function
  end

end

# Squares.new(5).square_of_sum

def test_difference_of_squares_0
# skip
assert_equal 0, Squares.new(0).difference
end