Write a program that can serve as a simple calculator. this calculator keeps track of a single number (of type double) that is called result and that starts out as 0.0. each cycle allows the user to repeatedly add, subtract, multiply, or divide by a second number. the result of one of these operations becomes the new value of result. the calculation ends when the user enters the letter r for "result" (either in uppercase or lowercase). the user is allowed to do another calculation from the beginning as often as he or she wants. use the scanner for input.