Question

I’m creating a small prime number program, and am confused about one thing.

I have a function called create_numbers, that generates numbers and passes them to a new function called check_for_primes, which passes only prime numbers to a final function called count_primes. I want to collect each prime into an array in the function count_primes, but for some reason each number is collected as its own array.

Any idea of what I’m doing wrong?

Here is the code:

def create_numbers
  nums = 1
  while nums < 100
    nums = nums + 2
    check_for_primes(nums)
  end  
end

def count_primes(nums)  
  array = []
  array << nums  
  puts array.inspect
end

def check_for_primes(nums)
    (2...nums).each do |i|
      if nums%i == 0
        nums = false
        break
      end
    end
    if nums != false
      count_primes(nums)
    end
end

create_numbers

Answer 1

Try this:

START = 1
STEP = 2

class Integer
  def prime?
    return if self < 2
    (2...self).each do |i|
      return if self % i == 0
    end
    true
  end
end

def create_numbers
  num = START
  while (num + STEP) < 100
    num += STEP
    primes << num if num.prime?
  end
end

def primes
  @primes ||= []
end

create_numbers
p primes

When you want to save the ‘state’ of something, put it in an instance variable (@var).
It’ll be accessible outside of the current function’s scope.

Also, try naming your variables differently. For instance, instead of ‘nums’, in the
create_numbers method, use ‘num’. Since the variable is only referencing one number at a
time and not a list of numbers, naming it in the plural will confuse people (me included)…

Hope it helps,

-Luke