8. Final Project: "Running Total" Calculator

• Your assignment is to build a small command-based arithmetic calculator.

• The calculator understands arithmetic operators + - * / % = followed by an integer:

      + 1 ; addition
      - 3 ; subtraction
      * 8 ; multiplication
      / 4 ; division
      % 2 ; modulo (remainder)
      = 5 ; assignment
  

  After each input the calculator does the required math and displays the result. The result is a running total: it is used in the next calculation. Lastly entered arithmetic operator is "sticky": the user can enter numbers without an operator to continue using the same operator. For example, (all user inputs are highlighted):

  0+ 10           ; addition is a default operation
          = 10
  10+ 10          ; user enters a number without an operator
          = 20
  20+ 10
          = 30
  30+ /3          ; the user wants to divide by 3
          = 10
  10/ 2           ; division becomes the default operation
          = 5
  5/ quit         ; quit exits the program