ask_for_number.rb

# frozen_string_literal: true
def get_input(prompt = '--> ')
  puts ''
  puts 'Please enter a number, odd or even.'
  print prompt
  # if the end-of-input was reached and gets returned a nil
  # or the word 'exit' or 'quit' appears (ignoring case) in the input
  if (input = gets).nil? || /exit|quit/i =~ input
    nil                         # just return a nil
  else
    input.to_i                  # otherwise, return the integer conversion
  end
end

def test_user_input(number)
  "'#{number}' is an #{number.even? ? 'EVEN' : 'odd'} number.\n"
end

while (number = get_input)      # while the number I capture from get_input isn't nil (or false)
  puts test_user_input(number)
end

Note that this is still not quite perfect as you can see by:

$ ruby ./ask_for_number.rb 

Please enter a number, odd or even.
--> 4
'4' is an EVEN number.

Please enter a number, odd or even.
--> 5
'5' is an odd number.

Please enter a number, odd or even.
--> nothing
'0' is an EVEN number.

Please enter a number, odd or even.
--> i quit

RegExp#match? doesn't exist in ruby 2.2.2 so use RegExp#=~ instead.