Ruby .each iteration clarification

Question

The questions asks: Write a method, is_prime?, that takes a number num and returns true if it is prime and false otherwise

'''ruby def is_prime?(num) (2...num).each do |d| return false if num % d == 0 end true end '''

My question is what is (2...num) process called? Also for example if i set is_prime?(2) what function does the placeholder |d| do?

thank you!

Answer 1 · 2014-01-30T17:20:42Z

January 30, 2014 5:20pm

I think you just want to do:

def is_prime(num)
    if num #add your check here
        return true
    else
        return false
    end
end

I don't think there is a reason to iterate here. You want the method to take in only one number, hence the "num"

Answer 2 · 2014-01-30T20:23:52Z

January 30, 2014 8:23pm

thanks for the reply brandon

So the first code that i had was:

def is_prime?(num) if num % 2 != 0 return true else return false end end

The problem I noticed with this code is that 2 will return a false statement when 2 is a prime number.

Answer 3 · 2014-01-31T03:18:51Z

January 31, 2014 3:18am

You could said that if

if num % 2 != 0 || num == 2

The only problem here is that being divisible by 2 is not the definition of prime. I see what you were doing originally. You were looking at all numbers from 2 to the number with 2..num, and if none of those actually divide into the number, then you are prime. You could actually change it to 2..(num -1 ) since we don't need to check num.

I would try

def is_prime(num)
  for d in 2..(num - 1)
   if (num % d) == 0
    return false
   end
  end

  true
 end

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Lawrence Chang

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Ruby .each iteration clarification

3 Answers

Brandon Barrette

Brandon Barrette

Lawrence Chang

Lawrence Chang

Brandon Barrette

Brandon Barrette