Objects in c++

1. C++
OBJECTS

2. Objects
 In C++, the class variables are called objects.
 An object is an instance of the class.
 Class is the passive entity while object is an
active entity.

3. Creating an object of a Class
 Declaring a variable of a class type creates an object. You can have
many variables of the same type (class).
 The memory space for the objects is allocated when they are
declared.
 When an object is created, space for that object is allocated in
primary memory.
 Space for member variables is allocated separately for each object.

4. Syntax
class_name object_name;
 Example: Things t1;
 To create multiple objects: Things t1,t2,t3;
 There can be multiple objects created from one class.

5. Objects…
 The objects can also be created when a class is defined by
placing their names immediately after the closing braces
like
Class Things
{
private:
… … …;
public:
… … …;
}t1,t2,t3;

6. Accessing Class Members
Operators to access class members
Identical to those for structs
Dot member selection operator (.)
Object
Reference to object
With objects we can access the public members of a
class using a dot operator.

7. Example:
#include <iostream.h>
class Box
{
public:
double length; // Length of a box
double breadth; // Breadth of a box
double height;// Height of a box
};
Void main( )
{
Box Box1; // Declare Box1 of type Box
Box Box2; // Declare Box2 of type Box
double volume = 0.0; // Store the volume of a box here
// box 1 specification
Box1.height = 5.0;
Box1.length = 6.0;
Box1.breadth = 7.0;
// box 2 specification
Box2.height = 10.0;
Box2.length = 12.0;
Box2.breadth = 13.0;
// volume of box 1
volume = Box1.height * Box1.length * Box1.breadth;
cout << "Volume of Box1 : " << volume <<endl;
// volume of box 2
volume = Box2.height * Box2.length * Box2.breadth;
cout << "Volume of Box2 : " << volume <<endl;
}
When the above code is compiled and executed, it produces the following result:
Volume of Box1 : 210
Volume of Box2 : 1560

8. Array of Objects
 Arrays of variables of type class are called arrays of objects.
Example:
class Employee
{
char name[20];
float age;
public:
void getdata(void);
void putdata(void);
};

9. For example:
Employee manager[3]; //array of manager
Employee worker[15]; // array of worker
Employee peon[2]; // array of peon
 The array manager contains three objects.
 The array worker contains 15 objects.
 The array peon contains two objects.
 They all contains the objects of the Employee class.

10. Objects as function argument
 Object can be used as a function argument. This can be done in two
method ways:
• A copy of the entire object is passed to the function.
• Only the address of the object is transferred to the function.
 The first method is called pass-by-value.
 The second method is called pass-by-reference.
 Pass-by-reference method is more effective.
 A function can also return an object.

11. //value.cpp
#include <iostream.h>
class test
{
int a;
public:
void set(test x)
{
x.a=5;
cout<<"a="<<x.a;
}
void show(test y)
{
cout<<"a="<<y.a;
}
};
void main()
{
test t;
t.set(t);
t.show(t);
}
//reference.cpp
#include <iostream.h>
class test
{
int a;
public:
void set(test *x)
{
x->a=5;
cout<<"a="<<x->a;
}
void show(test *y)
{
cout<<"a="<<y->a;
}
};
void main()
{
test t;
t.set(&t);
t.show(&t);

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