From: Peter Hickman <peterhickman386@...>
Date: 2012-04-13T22:09:59+09:00
Subject: Re: Arguments with Funktion

Firstly argument a is not needed as you do not use it.

Secondly there are several prime numbers between 2 and 50 so you
should be returning a list.

Here is a quick hack of your code

b = 50 # ARGV

def prime(b)
  prime_numbers = Array.new

  for i in 2..b
    f=true
    for p in 2...i
      if i%p==0
        f = false
        break
      end
    end
    prime_numbers << i if f
  end

  prime_numbers
end

sushu=prime(b)
p "the prime between 2 and #{b} are #{sushu.inspect}."

How lets make it a bit more Rubyish and readable...

def prime(upper_limit)
  prime_numbers = Array.new

  (2..upper_limit).each do |number_to_check|
    is_a_prime_number = true
    (2...number_to_check).each do |factor|
      if number_to_check % factor == 0
        is_a_prime_number = false
        break
      end
    end
    prime_numbers << number_to_check if is_a_prime_number
  end

  prime_numbers
end

Now lets mix in Jan E. suggested code

def prime(upper_limit)
  prime_numbers = Array.new

  2.upto upper_limit do |number_to_check|
    prime_numbers << number_to_check unless (2...number_to_check).any?
{|factor| number_to_check % factor == 0}
  end

  prime_numbers
end

Actually there are better ways to check for prime numbers between a
and b (hint: 2 is the only *even* prime, why are you even looking at
any others?)