1. Introduction to Classes and Objects
CHAPTER 5
Introduction to Classes and Objects

2. Review: Two Programming Paradigms
Structural (Procedural) Object-Oriented
PROGRAM PROGRAM
OBJECT
Operations
Data
FUNCTION
FUNCTION
OBJECT
Operations
Data
A list of tasks to perform.
Viewed as a collection of interacting objects. Each object can be viewed as an independent machine with a distinct role or responsibility. Operations are closely associated with the objects, carry their own operators around with them .
OBJECT
Operations
Data
FUNCTION
Function calls
Messages passing

3. Review: C++ Data Types simple structured address integral enum
floating
float double long double
array struct union class
char short int long bool
address
pointer reference

4. Classes & Objects The class is the cornerstone of C++ Class: Object:
It gives the C++ its identity from C
It makes possible encapsulation, data hiding and inheritance
Class:
Consists of both data and methods
Defines properties and behavior of a set of entities
Object:
An instance of a class
A variable identified by a unique name
Aim of class: a) provide the programmer with a tool for creating new types that can be used as conveniently as the built-in types (like float) b) user-defined type
why? Separate the incidental details of the implementation from the properties essential to the correct use of it
2. Derived class, templates: organizing related classes that allow the programmer to take advantage of their relationships.

5. Define a Class Type class Rectangle { private: int width; int length;
public:
void set(int w, int l);
int area(); };
class class_name {
permission_label:
member;
... };
Header
Body

7. Defining a member function with a parameter
#include <iostream.h>
class circle {
private:
double radius;
public:
void store(double);
double area(void);
void display(void); };
// member function definitions
void circle::store(double r) {
radius = r; }
double circle::area(void)
return 3.14*radius*radius;
void circle::display(void)
cout << “r = “ << radius << endl;
int main(void) {
circle c; // an object of circle class
c.store(5.0);
cout << "The area of circle c is " << c.area() << endl;
c.display(); }

8. Constructors
Constructor:– a function used to initialize the data of an object of a class
Same name as class itself
Cannot return anything, not even void
A class may define more than one constructor
With different parameter lists
Default constructor has no parameters
Called automatically
When class object is declared as automatic variable
By new operator

9. Constructor Example
Constructor has same name as class and no return type
Initialize data member

10. Constructor Example
Destructor need so this class object can free dynamically allocated memory

11. Creating objects implicitly calls the constructor
Constructor Example
Creating objects implicitly calls the constructor

12. Defining the constructor
class Circle {
private:
double radius;
public:
Circle();
Circle(int r);
void setRadius(double r);
double getDiameter();
double getArea();
double getCircumference(); };
Constructor with no argument – Default Constructor
Constructor with one argument

13. Destructors
Destructor:– a function used to clean up an object of a class prior to deleting that object
Class name preceeded by '~'
No parameters, no result
Called automatically
When function exits scope of automatic class object
By delete operator

14. Destructors Example class string { private: char *s; int size; public:
string(char *); // constructor
~string(); // destructor };
string::string(char *c) {
size = strlen(c);
s = new char[size+1];
strcpy(s,c); }
string::~string()
delete []s;

15. Composition: Objects as member of classes
What is an object?
OBJECT
set of methods
(public member functions)
internal state
(values of private data members)
Operations
Data

16. Declaration of an Object
class Rectangle {
private:
int width;
int length;
public:
void set(int w, int l);
int area(); }
main() {
Rectangle r1;
Rectangle r2;
r1.set(5, 8);
cout<<r1.area()<<endl;
r2.set(8,10);
cout<<r2.area()<<endl; }

17. Example #include <iostream.h> // member function definitions
class circle {
private:
double radius;
public:
void store(double);
double area(void);
void display(void); };
// member function definitions
void circle::store(double r) {
radius = r; }
double circle::area(void)
return 3.14*radius*radius;
void circle::display(void)
cout << “r = “ << radius << endl;
int main(void) {
circle c; // an object of circle class
c.store(5.0);
cout << "The area of circle c is " << c.area() << endl;
c.display(); }