Search⌘ K
AI Features
Home
Courses
Discover Ruby Programming Through Fun Examples

Solution: Finding Prime Numbers

Explore how to find prime numbers in Ruby by focusing on checking a single number's primality, using flag variables and loops effectively. Understand the importance of addressing core logic before expanding to broader loops, building foundational skills for better code organization and problem-solving in programming.

We'll cover the following...

Solution

Ruby 3.1.2
array = [] 
(2..20).each do |num|
  # check if num is a prime number or not
  flag = true
  (2..num - 1).each do |x| # check each possible divisor
    if num % x == 0
      flag = false # mark this has divisor
      break # no point to check more - composite, moves on to next
    end 
  end
  if flag == true # the number has no divisors 
    array << num # add to prime number list
  end 
end
puts "Prime numbers (up to 20) are : #{array.join(', ')}"

Explanation

  • Line 4: Initially, flag is set to true and every number is considered a prime number.

  • Line 7: If the number has a divisor, then flag is set to false to indicate that it is not a prime.

  • ...