def caesar_cipher(str, shift = 5)
  alpha = ('a'..'z').to_a
  shifted = []

  str = str.split('')
  str.each do |e|
    if e =~ /[A-Za-z]/
      e == e.downcase ? shifted << alpha[alpha.index(e) - shift] : shifted << alpha[alpha.index(e)].upcase
    else
      shifted << e
    end
  end

  shifted.join
end