calculator.rb

print "the first number: "
a = gets.chomp
print "operator: "
operator = gets.chomp
print "the second number: "
b = gets.chomp

answer = case operator.ord
  when 43 then a.to_i + b.to_i
  when 45 then a.to_i - b.to_i
  when 42 then a.to_i * b.to_i
  when 47 then a.to_f / b.to_f
  else 
    "error"
  end

puts "answer: #{answer}"