calculator.rb

POSSIBLE_OPERATORS = %w(* / + - %)

def process_calculation(first_number, second_number, operator)
  return nil unless POSSIBLE_OPERATORS.include? operator
  # case operator
  # when "+"
  #   first_number.+(second_number)
  # when "-"
  #   first_number.-(second_number)
  # when "*"
  #   first_number.*(second_number)
  # when "/"
  #   first_number./(second_number)
  # end

  first_number.send(operator, second_number)
end

interface.rb

require_relative "calculator"

continue = "y"

while continue.start_with? "y"
  print "operand> "
  first_number = gets.chomp.to_i

  operator = nil
  until POSSIBLE_OPERATORS.include? operator
    print "operator (#{POSSIBLE_OPERATORS.join(', ')})> "
    operator = gets.chomp
  end

  print "operand> "
  second_number = gets.chomp.to_i

  result = process_calculation(first_number, second_number, operator)

  puts "Result: #{result}"

  print "continue? (Y/N)> "
  continue = gets.chomp.downcase
end

puts "Bye bye"