1. Starting Out with C++: Early Objects 5th Edition
Chapter 7
Structured Data and Classes
Starting Out with C++: Early Objects 5/e
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2. Topics 7.1 Combining Data into Structures
7.2 Accessing Structure Members
7.3 Initializing a Structure
7.4 Nested Structures
7.5 Structures as Function Arguments
7.6 Returning a Structure from a Function
7.7 Unions
7.8 Abstract Data Types
7.9 Object-Oriented Programming
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Chapter 7 Starting Out with C++: Early Objects 5/e
slide 2

3. Topics (Continued) 7.10 Introduction to Classes
7.11 Introduction to Objects
7.12 Defining Member Functions
7.13 Design Considerations
7.14 Using a Constructor with a Class
7.15 Overloading Constructors
7.16 Destructors
7.17 Input Validation Objects
7.18 Using Private Member Functions
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Chapter 7 Starting Out with C++: Early Objects 5/e
slide 3

4. 7.1 Combining Data into Structures
Structure: C++ construct that allows multiple variables to be grouped together
Structure Declaration Format:
struct structure name {
type1 field1;
type2 field2; …
typen fieldn; };
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slide 4

5. Example struct Declaration
struct Student {
int studentID;
string name;
short year;
double gpa; };
structure tag
structure members
Notice the required ;
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Chapter 7 Starting Out with C++: Early Objects 5/e
slide 5

6. struct Declaration Notes
struct names commonly begin with an uppercase letter
Multiple fields of same type can be in a comma-separated list
string name,
address;
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slide 6

7. Defining Structure Variables
struct declaration does not allocate memory or create variables
To define variables, use structure tag as type name
Student s1;
studentID
name
year
gpa s1
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slide 7

8. 7.2 Accessing Structure Members
Use the dot (.) operator to refer to members of struct variables
getline(cin, s1.name);
cin >> s1.studentID;
s1.gpa = 3.75;
Member variables can be used in any manner appropriate for their data type
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slide 8

9. Displaying struct Members
To display the contents of a struct variable, you must display each field separately, using the dot operator
Wrong:
cout << s1; // won’t work!
Correct:
cout << s1.studentID << endl;
cout << s1.name << endl;
cout << s1.year << endl;
cout << s1.gpa;
See pr7-01.cpp and pr7-02.cpp
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Chapter 7 Starting Out with C++: Early Objects 5/e
slide 9

10. 7.3 Initializing a Structure
Cannot initialize members in the structure declaration, because no memory has been allocated yet
struct Student // Illegal
{ // initialization
int studentID = 1145;
string name = "Alex";
short year = 1;
float gpa = 2.95; };
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slide 10

11. Initializing a Structure (continued)
Structure members are initialized at the time a structure variable is created
Can initialize a structure variable’s members with either
an initialization list
a constructor
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slide 11

12. Using an Initialization List
An initialization list is an ordered set of values, separated by commas and contained in { }, that provides initial values for a set of data members
{12, 6, 3} // initialization list
// with 3 values
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13. More on Initialization Lists
Order of list elements matters: First value initializes first data member, second value initializes second data member, etc.
Elements of an initialization list can be constants, variables, or expressions
{12, W, L/W + 1} // initialization list
// with 3 items
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14. Initialization List Example
Structure Declaration Structure Variable
struct Dimensions
{ int length,
width,
height; };
Dimensions box = {12,6,3};
box
length 12
width 6
height 3
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15. Partial Initialization
Can initialize just some members, but cannot skip over members
Dimensions box1 = {12,6}; //OK
Dimensions box2 = {12,,3}; //illegal
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16. Problems with Initialization List
Can’t omit a value for a member without omitting values for all following members
Does not work on most modern compilers if the structure contains any string objects
Will, however, work with C-string members
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17. Using a Constructor to Initialize Structure Members
A constructor is a special function that can be a member of a structure
It is normally written inside the struct declaration
Its purpose is to initialize the structure’s data members
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18. Using a Constructor (continued)
Unlike most functions, a constructor is not called; instead, it is automatically invoked when a structure variable is created
The constructor name must be the same as the structure name (i.e. the struct tag)
The constructor must have no return type
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19. A Structure with a Constructor
struct Dimensions {
int length,
width,
height;
// Constructor
Dimensions(int L, int W, int H)
{length = L; width = W; height = H;} };
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20. Passing Arguments to a Constructor
Create a structure variable and follow its name with an argument list
Example:
Dimensions box3(12, 6, 3);
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21. Default Arguments
A constructor may be written to have default arguments
struct Dimensions {
int length,
width,
height;
// Constructor
Dimensions(int L=1, int W=1, int H=1)
{length = L; width = W; height = H;} };
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22. Omit () when no arguments are used
Examples
//Create a box with all dimensions given
Dimensions box4(12, 6, 3);
//Create a box using default value 1 for
//height
Dimensions box5(12, 6);
//Create a box using all default values
Dimensions box6;
See pr7-03.cpp
Omit () when no arguments are used
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slide 22

23. 7.4 Nested Structures A structure can have another structure as a
member.
struct PersonInfo
{ string name,
address,
city; };
struct Student
{ int studentID;
PersonInfo pData;
short year;
double gpa;
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24. Members of Nested Structures
Use the dot operator multiple times to dereference fields of nested structures
Student s5;
s5.pData.name = "Joanne";
s5.pData.city = "Tulsa";
See pr7-04.cpp
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slide 24

25. 7.5 Structures as Function Arguments
May pass members of struct variables to functions
computeGPA(s1.gpa);
May pass entire struct variables to functions
showData(s5);
Can use reference parameter if function needs to modify contents of structure variable
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26. Notes on Passing Structures
Using a value parameter for structure can slow down a program and waste space
Using a reference parameter speeds up program, but allows the function to modify data in the structure
To save space and time, while protecting structure data that should not be changed, use a const reference parameter
void showData(const Student &s)
// header
See pr7-05.cpp
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slide 26

27. 7.6 Returning a Structure from a Function
Function can return a struct
Student getStuData(); // prototype
s1 = getStuData(); // call
Function must define a local structure
for internal use
to use with return statement
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28. Returning a Structure Example
Student getStuData()
{ Student s; // local variable
cin >> s.studentID;
cin.ignore();
getline(cin, s.pData.name);
getline(cin, s.pData.address);
getline(cin, s.pData.city);
cin >> s.year;
cin >> s.gpa;
return s; }
See pr7-06.cpp
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Chapter 7 Starting Out with C++: Early Objects 5/e
slide 28

29. 7.7 Unions Similar to a struct, but Declared using key word union
all members share a single memory location
(which saves space)
only 1 member of the union can be used at a
time
Declared using key word union
Otherwise the same as struct
Variables defined and accessed like struct variables
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30. Example union Declaration
union WageInfo {
double hourlyRate;
float annualSalary; };
union tag
union members
See pr7-07.cpp
Notice the required ;
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31. Anonymous Union A union without a tag:
With no tag you cannot create additional union variables of this type later
Allocates memory at declaration time
Refer to members directly without dot operator
See pr7-08.cpp
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32. 7.8 Abstract Data Types A programmer-created data type that specifies
legal values that can be stored
operations that can be done on the values
The user of an abstract data type does not need to know any implementation details (e.g., how the data is stored or how the operations on it are carried out)
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33. Abstraction and Data Types
Abstraction: a definition that captures general characteristics without details
Ex: abstract triangle is a 3-sided polygon. A specific triangle may be scalene, isosceles, or equilateral
Data Type: defines the kind of values that can be stored in a variable and the operations that can be performed on it
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34. 7.9 Object-Oriented Programming
Procedural programming focuses on the process/actions that occur in a program
Object-Oriented programming is based on the data and the functions that operate on it. Objects are instances of Abstract Data Types, or ADTs.
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35. Limitations of Procedural Programming
Use of global data may allow data corruption
Programs are often based on complex function hierarchies
difficult to understand and maintain
difficult to modify and extend
easy to break
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36. Object-Oriented Programming Terminology
class: similar to a struct
Allows bundling of related variables (member data) and the functions that operate on them (member functions)
Describes the properties that all instances of the class will have
object: an instance of a class, in the same way that a variable can be an instance of a struct
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37. More Object-Oriented Programming Terminology
attributes: member data of a class
methods or behaviors: member functions of a class
data hiding: restricting access to certain members of an object
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38. Public Interface
Class objects are accessed from outside the class via a public interface
This is done by allowing some of the member functions to be called from outside the class
Normally, all the class’s member variables are accessed only through these “public” functions
This provides some protection from data corruption
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39. 7.10 Introduction to Classes
A class declaration describes the member variables and member functions that its objects will have
It is a pattern for creating objects
Class Declaration Format:
class className {
declaration; };
Notice the required ;
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40. Access Specifiers
Used to control access to members of the class. Each member is declared to be either
public: can be accessed by functions
outside of the class or
private: can only be called by or accessed
by functions that are members of
the class
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41. Class Example class Square { private: int side; public:
void setSide(int s)
{ side = s; }
int getSide()
{ return side; } };
Access specifiers
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42. More on Access Specifiers
Can be listed in any order in a class
Can appear multiple times in a class
If not specified, the default is private
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43. 7.11 Introduction to Objects
An object is an instance of a class
Defined like structure variables
Square sq1, sq2;
Access members using dot operator
sq1.setSide(5);
cout << sq2.getSide();
Compiler error if attempt to access private member using dot operator
See pr7-09.cpp
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44. 7.12 Defining Member Functions
Member functions are part of a class declaration
Can place entire function definition inside the class declaration or
Can place just the prototype inside the class declaration and write the function definition after the class
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45. Defining Member Functions Inside the Class Declaration
Member functions defined inside the class declaration are called inline functions
Only very short functions, like the one below, should be inline functions
int getSide()
{ return side; }
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46. Inline Member Function Example
class Square {
private:
int side;
public:
void setSide(int s)
{ side = s; }
int getSide()
{ return side; } };
inline functions
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47. Defining Member Functions After the Class Declaration
To define a member function after the class declaration
Put a function prototype in the class declaration
In the function definition, precede function name with class name and scope resolution operator (::)
int Square::getSide() {
return side; }
See pr7-10.cpp and pr7-11.cpp
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48. Tradeoffs of Inline vs. Regular Member Functions
When a regular function is called, control passes to the called function
the compiler stores return address of call, allocates memory for local variables, etc.
Code for an inline function is copied into the program in place of the call
larger executable program, but
no function call overhead, possibly faster execution
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49. 7.13 Design Considerations
Class should be designed to provide functions to store and retrieve data
In general, I/O should be done by functions that use class objects, rather than by class member functions (Exceptions can occur, as with a class designed to display a menu)
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50. More Design Considerations
Separating class declaration, member function definitions, and program that uses the class into separate files is considered good design
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51. Using Separate Files
Place class declaration in a header file that serves as the class specification file. Name the file classname.h (for example, Square.h)
Place member function definitions in a class implementation file. Name the file classname.cpp (for example, Square.cpp)This file should #include the class specification file.
Programs that use the class must #include the class specification file and be compiled and linked with the class implementation file.
See pr7-12.cpp, rectangle.cpp, and rectangle.h
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slide 51

52. 7.14 Using a Constructor with a Class
As with a structure, a constructor can be used to initialize data members of a class
Must be a public member function
Must be named the same as the class
Must have no return type
Is called automatically when an object of the class is created
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slide 52

53. The Default Constructor
Constructors can have any number of parameters, including none
A default constructor is one that takes no arguments either due to
No parameters or
All parameters have default values
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54. Default Constructor Example
class Square {
private:
int side;
public:
Square() // default
{ side = 1; } // constructor
// Other member
// functions go here };
Has no
parameters
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55. Another Default Constructor Example
class Square {
private:
int side;
public:
Square(int s = 1) // default
{ side = s; } // constructor
// Other member
// functions go here };
Has parameter
but it has a default value
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56. Invoking a Constructor
Invoking a constructor for a class object is done just like invoking a constructor for a structure variable
To create an object using the default constructor, use no argument list and no ()
Square square1;
To create an object using a constructor that has parameters, include an argument list
Square square1(8);
See pr7-13.cpp
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slide 56

57. 7.15 Overloading Constructors
A class can have > 1 constructor
Overloaded constructors in a class must have different parameter lists
Square();
Square(int);
Only one default constructor is allowed
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58. Member Function Overloading
Non-constructor member functions can also be overloaded
void setSide();
void setSide(int);
Must have unique parameter lists (as with constructors)
See pr7-14.cpp and sale.h
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slide 58

59. 7.16 Destructors
Public member function automatically called when an object is destroyed
Destructor name is ~className, e.g., ~Square
Has no return type
Takes no arguments
Only 1 destructor is allowed per class
(i.e., it cannot be overloaded)
See pr7-15.cpp
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60. 7.17 Input Validation Objects
Objects can be designed to validate user input
to ensure acceptable menu choice
to ensure a value is in range of valid values
etc.
See pr7-16.cpp, CharRange.cpp, and CharRange.h
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slide 60

61. 7.18 Using Private Member Functions
A private member function can only be called by another member function of the same class
It is used for internal processing by the class, not for use outside of the class
See pr7-17.cpp
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Chapter 7 Starting Out with C++: Early Objects 5/e
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62. Starting Out with C++: Early Objects 5th Edition
Chapter 7
Structured Data and Classes
Starting Out with C++: Early Objects 5/e
© 2006 Pearson Education.
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