caesar_cipher.rb

#!/usr/bin/env ruby
class Integer
    @@range_upper = (65..90)
    @@range_lower = (97..122)

    def upper?
        @@range_upper.include? self
    end

    def lower?
        @@range_lower.include? self
    end

    def self.max_upper
        @@range_upper.max
    end

    def self.max_lower
        @@range_lower.max
    end
end

def caesar(text,shift)
    result = ""
    text.each_char do |letter|
        sequence = letter.ord
        if sequence.upper?
            next_letter = sequence + shift
            next_letter -= 26 if next_letter > Integer.max_upper
        elsif sequence.lower?
            next_letter = sequence + shift
            next_letter -= 26 if next_letter > Integer.max_lower
        else
            next_letter = sequence
        end
        result += next_letter.chr
    end
    return result
end

puts caesar("What a String!",5)