Check the input is "y" or "n", or not.

yes_or_no.rb

loop do
        answer = gets.chomp
        if answer == "y"
                puts "You choose yes. See you."
                break;
        elsif answer == "n"
                puts "You choose no. See you."
                break;
        else
                puts "You typed #{answer} , you must type y or n."
        end
end