simple ruby class for testing primaility.

naive_primes.rb

class PrimesTester

  def initialize number
    @number = number
  end

  attr_accessor :number

  def prime?
    # test primaility for the input number.
    i = 2
    until i > @number / 2
      if @number % i == 0 then
        return false
      end
      i += 1
    end
    return true
  end

  def list_primes_under
    # determines each prime under the number attribute.
    puts "Lits of primes less than #{@number}: \n------------\n"
    i = 1

    while i <= @number
      is_prime = true

      j = 2
      while j <= i / 2
        if i % j == 0
          is_prime = false
          break
        end
        j += 1  
      end
      if is_prime then
        print " #{i} "
      end
      i += 1
    end
    puts "\n------------"
  end
end

p = PrimesTester.new 100
puts p.prime? 

p.number = 17
puts p.prime?

p.number = 25
p.list_primes_under