class Calculator
  def main()
    print( "Falcon Calculator" )
    while true
      print( "Enter first number: " )
      a = stdin.readln().to_number()
      print( "Enter operator: " )
      op = stdin.readln()
      print( "Enter second number: " )
      b = stdin.readln().to_number()
      if op == "+"
        print( "Result: ", a + b )
      elif op == "-"
        print( "Result: ", a - b )
      elif op == "*"
        print( "Result: ", a * b )
      elif op == "/"
        print( "Result: ", a / b )
      else
        print( "Invalid operator" )
      end
    end
  end
end

Calculator().main()