1. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 1 Chapter 10 Class Design

2. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 2 Objectives F To process strings using the string class (§10.2). F To develop functions with object arguments (§§10.3-4). F To store and process objects in arrays (§§10.5-6). F To distinguish between instance and static variables and functions (§10.7). F To define constant functions to prevent data fields from being modified accidentally (§10.8). F To explore the differences between the procedural paradigm and object-oriented paradigm (§10.9). F To design a class for body mass index (§10.9). F To develop classes for modeling composition relationships (§10.10). F To design a class for a stack (§10.11). F To describe the software life cycle (§10.12). F To design classes that follow the class-design guidelines (§10.13).

3. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 3 The C++ string Class

4. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 4 Constructing a String You can create an empty string using string’s no-arg constructor like this one: string newString; You can create a string object from a string value or from an array of characters. To create a string from a string literal, use a syntax like this one: string newString(stringLiteral);

5. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 5 Appending a String You can use several overloaded functions to add new contents to a string. For example, see the following code: string s1("Welcome"); s1.append(" to C++"); // appends " to C++" to s1 cout << s1 << endl; // s1 now becomes Welcome to C++ string s2("Welcome"); s2.append(" to C and C++", 0, 5); // appends " to C" to s2 cout << s2 << endl; // s2 now becomes Welcome to C string s3("Welcome"); s3.append(" to C and C++", 5); // appends " to C" to s3 cout << s3 << endl; // s3 now becomes Welcome to C string s4("Welcome"); s4.append(4, 'G'); // appends "GGGG" to s4 cout << s4 << endl; // s4 now becomes WelcomeGGGG

6. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 6 Assigning a String You can use several overloaded functions to assign new contents to a string. For example, see the following code: string s1("Welcome"); s1.assign("Dallas"); // assigns "Dallas" to s1 cout << s1 << endl; // s1 now becomes Dallas string s2("Welcome"); s2.assign("Dallas, Texas", 0, 5); // assigns "Dalla" to s2 cout << s2 << endl; // s2 now becomes Dalla string s3("Welcome"); s3.assign("Dallas, Texas", 5); // assigns "Dalla" to s3 cout << s3 << endl; // s3 now becomes Dalla string s4("Welcome"); s4.assign(4, 'G'); // assigns "GGGG" to s4 cout << s4 << endl; // s4 now becomes GGGG

7. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 7 Functions at, clear, erase, and empty You can use the at(index) function to retrieve a character at a specified index, clear() to clear the string, erase(index, n) to delete part of the string, and empty() to test if a string is empty. For example, see the following code: string s1("Welcome"); cout << s1.at(3) << endl; // s1.at(3) returns c cout << s1.erase(2, 3) << endl; // s1 is now Weme s1.clear(); // s1 is now empty cout << s1.empty() << endl; // s1.empty returns 1 (means true)

8. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 8 Comparing Strings Often, in a program, you need to compare the contents of two strings. You can use the compare function. This function works in the same way as the C-string strcmp function and returns a value greater than 0, 0, or less than 0. For example, see the following code: string s1("Welcome"); string s2("Welcomg"); cout << s1.compare(s2) << endl; // returns -2 cout << s2.compare(s1) << endl; // returns 2 cout << s1.compare("Welcome") << endl; // returns 0

9. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 9 Obtaining Substrings You can obtain a single character from a string using the at function. You can also obtain a substring from a string using the substr function. For example, see the following code: string s1("Welcome"); cout << s1.substr(0, 1) << endl; // returns W cout << s1.substr(3) << endl; // returns come cout << s1.substr(3, 3) << endl; // returns com

10. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 10 Searching in a String You can use the find function to search for a substring or a character in a string. For example, see the following code: string s1("Welcome to HTML"); cout << s1.find("co") << endl; // returns 3 cout << s1.find("co", 6) << endl; // returns -1 cout << s1.find('o') << endl; // returns 4 cout << s1.find('o', 6) << endl; // returns 9

11. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 11 Inserting and Replacing Strings Here are the examples to use the insert and replace functions: string s1("Welcome to HTML"); s1.insert(11, "C++ and "); cout << s1 << endl; // s1 becomes Welcome to C++ and HTML string s2("AA"); s2.insert(1, 4, 'B'); cout << s2 << endl; // s2 becomes to ABBBBA string s3("Welcome to HTML"); s3.replace(11, 4, "C++"); cout << s3 << endl; // returns Welcome to C++

12. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 12 String Operators

13. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 13 Reading Strings string city; cout << "Enter a city: "; cin >> city; // Read to array city cout << "You entered " << city << endl; string city; cout << "Enter a city: "; getline(cin, city, '\n'); // Same as getline(cin, city) cout << "You entered " << city << endl;

14. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 14 Passing Objects to Functions You can pass objects by value or by reference. Run PassObjectByValue PassObjectByReference

15. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 15 Checking Palindromes A string is a palindrome if it reads the same forward and backward. The words “mom,” “dad,” and “noon,” for example, are all palindromes. How do you write a program to check whether a string is a palindrome? Run CheckPalindrome

16. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 16 Array of Objects Circle circleArray[3] = {Circle(3), Circle(4), Circle(5)}; Run TotalArea

17. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 17 Improving Deck of Cards Solution §7.2.7 presented a program that picks four cards randomly from a deck of 52 cards. The program uses two functions displayRank and displaySuit to display a rank and a suit. These two functions can be replaced by defining the ranks and suits in two arrays of strings. Run DeckOfCards

18. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 18 Instance and Static Members Run TestCircle5.cppCircle5.h Circle5.cpp

19. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 19 Use Class Name Use ClassName::functionName(arguments) to invoke a static function and ClassName::staticVariable. This improves readability because the user can easily recognize the static function and data in the class.

20. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 20 Instance or Static? How do you decide whether a variable or function should be instance or static? A variable or function that is dependent on a specific instance of the class should be an instance variable or function. A variable or function that is not dependent on a specific instance of the class should be a static variable or function. For example, every circle has its own radius. Radius is dependent on a specific circle. Therefore, radius is an instance variable of the Circle class. Since the getArea function is dependent on a specific circle, it is an instance function. Since numberOfObjects is not dependent on any specific instance, it should be declared static.

21. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 21 Constant Member Functions You can use the const keyword to specify a constant parameter to tell the compiler that the parameter should not be changed in the function. C++ also enables you to specify a constant member function to tell the compiler that the function should not change the value of any data fields in the object. To do so, place the const keyword at the end of the function header. Circle4.h Circle4.cpp

22. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 22 Object-Oriented Thinking The book introduced fundamental programming techniques for problem solving using loops, functions, and arrays. The study of these techniques lays a solid foundation for object-oriented programming. Classes provide more flexibility and modularity for building reusable software. This section improves the solution for a problem introduced in Chapter 3 using the object- oriented approach. From the improvements, you will gain insight on the differences between the procedural programming and object-oriented programming and see the benefits of developing reusable code using objects and classes.

23. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 23 The BMI Class UseBMIClassRunBMI.cpp BMI.h

24. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 24 Example: The Course Class TestCourceRunCourse

25. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 25 Example: The StackOfIntegers Class Run TestStackOfIntegers

26. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 26 Designing the StackOfIntegers Class

27. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 27 Implementing StackOfIntegers Class StackOfIntegers

28. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 28 Object-Oriented Thinking Procedural vs. Object-Oriented Run BMI.h BMI.cpp TestPerson

29. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 29 Object Composition Composition is actually a special case of the aggregation relationship. Aggregation models has-a relationships and represents an ownership relationship between two objects. The owner object is called an aggregating object and its class an aggregating class. The subject object is called an aggregated object and its class an aggregated class.

30. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 30 Class Representation An aggregation relationship is usually represented as a data field in the aggregating class. For example, the relationship in Figure 10.6 can be represented as follows:

31. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 31 Aggregation or Composition Since aggregation and composition relationships are represented using classes in similar ways, many texts don’t differentiate them and call both compositions.

32. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 32 The StackOfInteger Class A stack is a data structure that holds objects in a last-in first-out fashion, as illustrated in Figure 10.10. It has many applications. For example, the compiler uses a stack to process function invocations. When a function is invoked, the parameters and local variables of the function are pushed into a stack. When a function calls another function, the new function’s parameters and local variables are pushed into the stack. When a function finishes its work and returns to its caller, its associated space is released from the stack.

33. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 33 The StackOfInteger Class

34. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 34 Class UML The StackOfIntegers class encapsulates the stack storage and provides the operations for manipulating the stack.

35. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 35 Implementation Run TestStackOfIntegers StackOfIntegers.hStackOfIntegers.cpp

36. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 36 Software Development Process

37. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 37 Requirement Specification A formal process that seeks to understand the problem and document in detail what the software system needs to do. This phase involves close interaction between users and designers. Most of the examples in this book are simple, and their requirements are clearly stated. In the real world, however, problems are not well defined. You need to study a problem carefully to identify its requirements.

38. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 38 System Analysis Seeks to analyze the business process in terms of data flow, and to identify the system’s input and output. Part of the analysis entails modeling the system’s behavior. The model is intended to capture the essential elements of the system and to define services to the system.

39. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 39 System Design The process of designing the system’s components. This phase involves the use of many levels of abstraction to decompose the problem into manageable components, identify classes and interfaces, and establish relationships among the classes and interfaces.

40. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 40 Implementation The process of translating the system design into programs. Separate programs are written for each component and put to work together. This phase requires the use of a programming language like Java. The implementation involves coding, testing, and debugging.

41. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 41 Testing Ensures that the code meets the requirements specification and weeds out bugs. An independent team of software engineers not involved in the design and implementation of the project usually conducts such testing.

42. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 42 Deployment Deployment makes the project available for use. For a Java applet, this means installing it on a Web server; for a Java application, installing it on the client's computer.

43. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 43 Maintenance Maintenance is concerned with changing and improving the product. A software product must continue to perform and improve in a changing environment. This requires periodic upgrades of the product to fix newly discovered bugs and incorporate changes.

44. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 44 Designing a Class: Cohesion F A class should describe a single entity or a set of similar operations. A single entity with too many responsibilities can be broken into several classes to separate responsibilities.

45. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 45 Designing a Class: Consistency F Follow standard programming style and naming conventions. Choose informative names for classes, data fields, and functions. A popular style in C++ is to place the data declaration after the functions, and place constructors before functions.

46. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 46 Designing a Class: Encapsulation F A class should use the private modifier to hide its data from direct access by clients. This makes the class easy to maintain. F Provide a get function only if you want the field to be readable, and provide a set function only if you want the field to be updateable. A class should also hide functions not intended for client use. Such functions should be defined as private.

47. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 47 Designing a Class: Clarity F Users can incorporate classes in many different combinations, orders, and environments. Therefore, you should design a class that imposes no restrictions on what or when the user can do with it, design the properties in a way that lets the user set them in any order and with any combination of values, and design functions independently of their order of occurrence. For example, the Loan class contains the functions setLoanAmount, setNumberOfYears, and setAnnualInterestRate. The values of these properties can be set in any order.

48. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 48 Designing a Class: Completeness F Classes are designed for use by many different customers. In order to be useful in a wide range of applications, a class should provide a variety of ways for customization through properties and functions. For example, the string class contains more than 20 functions that are useful for a variety of applications.

49. Liang, Introduction to Programming with C++, Second Edition, (c) 2010 Pearson Education, Inc. All rights reserved. 0136097200 49 Designing a Class: Instance vs. Static F A variable or function that is dependent on a specific instance of the class should be an instance variable or function. A variable that is shared by all the instances of a class should be declared static. For example, the variable numberOfObjects in Circle in Listing 10.9, is shared by all the objects of the Circle class, and therefore is declared static. A function that is not dependent on a specific instance should be declared as a static function. For instance, the getNumberOfObjects function in Circle is not tied to any specific instance, and therefore is declared as static functions.