caesar_cipher.rb

def caesar_cipher(message, key)
  
  alphabet = [*"a".."z"]
  alphabet_cifred = alphabet[key..26] + alphabet[0..key]

  c_array = message.split('')
  
  c_lambda = lambda  {
    |c|
    upper = c == c.upcase
    if alphabet.index(c.downcase)
      character = alphabet_cifred[alphabet.index(c.downcase)]
      upper ? character.upcase : character
    else
      c
    end
  }

  c_array.map(&c_lambda).join('')

end

puts caesar_cipher("What a string!", 5)