app_academy_practice.rb

require 'pry'

def pow base, exponent
  raise 'Params must be non-negative integers' if base < 0
  raise 'Params must be non-negative integers' if exponent < 0
  
  product = base

  if exponent == 1
    return base
  elsif exponent == 0
    return 1
  else
    return base * pow(base, exponent-1)
  end
end

#puts pow(2,15)


def summation array_of_numbers  #This method will take an array_of_numbers and return their sum
  if array_of_numbers.empty?
    return 0
  else
    digit = array_of_numbers.pop
    return digit + summation(array_of_numbers)
  end
end

#puts summation([4,5,6])

def is_prime? num  #takes a number num and returns true if it is prime and false otherwise.
  for test in 2..(Math.sqrt(num))
    if (num % test) == 0
      return false
    end
  end
  return true
end

#puts is_prime?(543)

# Q4: Using your is_prime? method, write a new method, 
# primes that takes a (non-negative, integer) number max
# and returns an array of all prime numbers less than max. 

def primes max
  array_of_primes = []
  for num in 2..(max)
    if is_prime?(num)
      array_of_primes << num
    end
  end
  return array_of_primes
end

puts primes(40).join(", ")