1. Chapter 9 Calculator

2. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-2 Chapter Objectives Provide a case study example from problem statement through implementation Demonstrate how a stack and a list can be used to solve a problem

3. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-3 A Calculator A calculator is a simple utility that is provided with most operating systems A calculator provides – a keypad of integer digits, – the associated operations, – other useful characters such as parentheses and brackets

4. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-4 A Calculator For this case study, we will create a graphical calculator that: – accepts an infix expression, – converts that expression to postfix, – evaluates the postfix expression, – returns the result

5. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-5 A Calculator Our infix expressions may include – Integers – Basic arithmetic operators addition, subtraction, multiplication, division – Parentheses All of the tokens in our expression must be separated by a space

6. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-6 A Calculator Our graphical user interface will allow the user to click on the numeric digits or simply press the numbers (and other characters) on the keyboard The user will click the equals button to start the evaluation of the given expression

7. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-7 A Calculator - Initial Design A calculator consists of four high-level components: – The driver – The graphical user interface – The infix to postfix converter – The postfix evaluator

8. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-8 A Calculator - Initial Design Unlike the BlackJack case study, these high-level components are virtually unrelated, and we are not yet aware of any low-level components that will be needed Thus this problem lends itself to a top- down approach to design

9. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-9 A Calculator - the CalculatorDemo Class The CalculatorDemo class will serve as the driver for our system This class will simply instantiate the GUI and call its display method

10. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-10 A Calculator - the CalculatorGUI Class Other than the driver, the GUI is the highest-level component in this system The GUI must provide buttons to represent the digits, the operations, parentheses, and an equals button

11. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-11 FIGURE 9.1 The calculator user interface

12. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-12 A Calculator - the infixToPostfix Class The purpose of the infixToPostfix class to to provide a conversion method that accepts an infix expression as a string and returns the equivalent postfix expression Since we know that the postfix expression will then be evaluated,we will return the postfix expression as an unordered list rather than a string

13. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-13

14. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-14 A Calculator - the listPostfixEvaluator Class Like our example from Chapter 6, the listPostfixEvaluator class will take the postfix expression and use a stack to evaluate it The difference from our earlier example is that the expression has already been broken into tokens by the infixToPostfix class

15. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-15 A Calculator - the listPostfixEvaluator Class

16. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 9-16 FIGURE 9.2 UML description of the initial design of a calculator