Unit 2: Object and Class (16)
2.1
Concept of Object and Class
2.2
Define Data Member and Member Function
2.3
Create object and access Member Function
2.4
Making outer function inline
2.5
Array with in Class
2.6
Array of Objects
2.7
Static Data Member and Static Function
2.8
Friends Functions
2.9
Concept of Constructor and Destructor
2.10 Empty, Parameterized and Copy
constructor
2.11 Define Destructor
Practical Works:
·
Create class and objects with data member and
member function.
·
Declare and define member function and data member
with visibility.
·
Create static function
·
Create friend functions.
·
Create different types of constructors
2.1 Concept of Object and Class
2073(2):
Explain the concept of class and object with examples.
Objects are the run-time
entities in object oriented system. Everything in C++ is associated with
classes and objects. Along with its attributes and methods. For example: in
real life, a car is an object. The car has attributes,
such as weight and color, and methods, such as drive and
brake.
Attributes and methods are
basically variables and functions that
belongs to the class. These are often referred to as "class members".
A class is a user-defined data
type that we can use in our program, and it works as an object constructor, or
a "blueprint" for creating objects.
Write a C++ Program to find Largest among 3 numbers using
classes and object
#include<iostream>using namespace std;class greatest{ private: int x,y,z; public: void input() { cout<<"Enter 3 nos."; cin>>x>>y>>z; } void calc() { int r; r=((x>y)&&(x>z)?x:(y>x)&&(y>z)?y:z); cout<<"Greatest no:"<<r; }};int main(){ greatest g; g.input(); g.calc(); } 2.2 Define Data Member and Member Function
Data member: 1. The variable declared inside class are known as data members.
2. Data member may be private or public.
Member function: 1. The functions declared inside the class are known as member functions.
2. Member functions are methods or functions that are defined inside of objects.
3. Generally used to manipulate data members and other object data.
#include<iostream>using namespace std;class student{ private: int id;// data member char name[20]; // data member public: void getdata(void)//member function void display(void)//member function { cout<<id<<’\t’<<name<<endl; } };int main(){ student s; s.getdata(void); s.display(void); }
2.3
Create object and access Member Function
Member
functions are the functions, which have their declaration inside the class
definition and works on the data members of the class. The definition of member
functions can be inside or outside the definition of class.
If the member
function is defined inside the class definition it can be defined directly, but
if its defined outside the class, then we have to use the scope resolution:: operator along with class name along
with function name.
For example:
class Cube
{
public:
int side;
/*
Declaring function getVolume
with no argument and return type int.
*/
int getVolume();
};
If we define
the function inside class then we don't not need to declare it first, we can
directly define the function.
class Cube
{
public:
int side;
int getVolume()
{
return side*side*side;
//returns volume of cube
}
};
But if we plan
to define the member function outside the class definition then we must declare
the function inside class definition and then define it outside.
class Cube
{
public:
int side;
int getVolume();
}
// member function defined outside
class definition
int Cube :: getVolume()
{
return side*side*side;
}
The main
function for both the function definition will be same. Inside main() we will
create object of class, and will call the member function using dot . operator.
2.4 Making outer function inline
Inline function is a function
that is expanded in line when it is called. When the inline function is called
whole code of the inline function gets inserted or substituted at the point of
inline function call. This substitution is performed by the C++ compiler at
compile time. Inline function may increase efficiency if it is small.
The syntax for defining the function inline is:
inline return-type function-name(parameters){ // function code}
The following
program demonstrates the use of use of inline function.
|
#include <iostream> using namespace std; inline int cube(int s) { return s*s*s; } int main() { cout <<
"The cube of 3 is: " << cube(3) << "\n"; return 0; } //Output: The cube of 3 is: 27 |
2.5 Array with in Class
Array can be declared as the member of a
class. The arrays can be declared as private, public or protected members of
class.
C++ provides a
data structure, the array, which stores a fixed-size sequential
collection of elements of the same type. An array is used to store a collection
of data, but it is often more useful to think of an array as a collection of
variables of the same type.
Instead of
declaring individual variables, such as number0, number1, ..., and number99,
you declare one array variable such as numbers and use numbers[0], numbers[1],
and ..., numbers[99] to represent individual variables. A specific element in
an array is accessed by an index.
All arrays
consist of contiguous memory locations. The lowest address corresponds to the
first element and the highest address to the last element.
Declaring Arrays
To declare an
array in C++, the programmer specifies the type of the elements and the number
of elements required by an array as follows −
type arrayName [ arraySize ];
This is called
a single-dimension array. The arraySize must be an integer constant
greater than zero and type can be any valid C++ data type. For example,
to declare a 10-element array called balance of type double, use this statement
−
double balance[10];
Initializing Arrays
You can
initialize C++ array elements either one by one or using a single statement as
follows −
double balance[5] = {1000.0, 2.0, 3.4,
17.0, 50.0};
The number of
values between braces { } can not be larger than the number of elements that we
declare for the array between square brackets [ ]. Following is an example to
assign a single element of the array −
If you omit the
size of the array, an array just big enough to hold the initialization is
created. Therefore, if you write −
double balance[] = {1000.0, 2.0, 3.4,
17.0, 50.0};
You will create
exactly the same array as you did in the previous example.
balance[4] = 50.0;
The above statement
assigns element number 5th in the array a value of 50.0. Array with
4th index will be 5th, i.e., last element because all
arrays have 0 as the index of their first element which is also called base
index. Following is the pictorial representaion of the same array we discussed
above −
Accessing Array Elements
An element is
accessed by indexing the array name. This is done by placing the index of the
element within square brackets after the name of the array. For example −
double salary = balance[9];
The above
statement will take 10th element from the array and assign the value
to salary variable.
A program to demonstrate the concept of arrays as class
members
Example:
#include<iostream> const int size=5; class student { int roll_no;int marks[size];public:void getdata ();void tot_marks ();} ; void student :: getdata (){cout<<"\nEnter roll no: ";Cin>>roll_no;for(int i=0; i<size; i++){cout<<"Enter marks in subject"<<(i+1)<<": ";cin>>marks[i] ;} void student :: tot_marks() //calculating total marks{int total=0;for(int i=0; i<size; i++)total+ = marks[i];cout<<"\n\nTotal marks "<<total;} void main()student stu;stu.getdata() ;stu.tot_marks() ;getch();}
Output:
Enter roll no: 101
Enter marks in subject 1: 67
Enter marks in subject 2 : 54
Enter marks in subject 3 : 68
Enter marks in subject 4 : 72
Enter marks in subject 5 : 82
Total marks = 343
2.6 Array of Objects
When a class is
defined, only the specification for the object is defined; no memory or storage
is allocated. To use the data and access functions defined in the class, you
need to create objects.
Syntax:
ClassName ObjectName[number of
objects];
The Array of
Objects stores objects. An array of a class type is also known as an
array of objects.
Example#1:
Storing more than one Employee data. Let’s assume there is an array of objects
for storing employee data emp[30].
|
#include<iostream> using namespace std; class Employee { int id; char name[30]; public: // Declaration of
function void getdata(); // Declaration of
function void putdata(); }; // Defining the function outside // the class void Employee::getdata() { cout << "Enter
Id : "; cin >> id; cout << "Enter
Name : "; cin >> name; } // Defining the function outside // the class void Employee::putdata() { cout << id <<
" "; cout << name
<< " "; cout << endl; } // Driver code int main() { // This is an array of
objects having // maximum limit of 30
Employees Employee emp[30]; int n, i; cout << "Enter
Number of Employees - "; cin >> n; // Accessing the function for(i = 0; i < n; i++) emp[i].getdata(); cout <<
"Employee Data - " << endl; // Accessing the function for(i = 0; i < n; i++) emp[i].putdata(); } |
Output:
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