Member Data and Member Functions

Member Data and Member Functions

• The data members and member function defined within a class belong to that class's scope.

• The non‒member functions belong to global namespace

• Within the class's scope, the data members of that class are immediately accessible by the member functions of that class.

• Outside the class the, only the public members of that class are accessible by handle. Following C++ program illustrates this concept.

C++ Program

#include <iostream>

using namespace std;

class Test

{

    //Public member functions of Class Test

  private:

    int a,b,c;

    public:

    int Addition(int a, int b)

    {

        c= a+b;

        return c;

    }

    void Display( )

    { cout << "The sum is:" << c << "\n";}

};

int main()

{

  //Accessing them outside the class using object of that class

    Test obj;

    obj.Addition(10,20);

    obj.Display();

    return 0;

}

• The class members are accessed using the handle called object with the help of dot operator. The ‒ > is used to access the pointer variable.

• There are two ways to access the class members.

Accessing class members:

1. Membersinside class

2. Members outside class

1. Accessing Class Members that are Defined Inside the Class

•  The function declared within the class is usually called as member function in C++ and it is called method in object oriented programming.

•  The data declared along with some data type is called as the data member of that class.

•  The data members denote the property of the class and the member functions denote the operations on that data.

•  Normally in C++ the data within the class is declared as private and member functions are declared as public. This avoids any manipulation of data by the functions outside the class. As these functions are declared as public they can be accessible from outside the class.

•  Some times you may require the data to be private and member functions to be public. Thus access mode helps the C++ programmer to hide the data whenever required.

• Following C++ program illustrates the concept of class, access specifiers, function and data members.

/*******************************************

Program to demonstrate the class, access specifiers and data and member functions

*******************************************/

#include <iostream>

using namespace std;

class Test

{

      private:

            int a,b,c;

      public:

      int Addition(int a, int b)

      {

            c = a+b;

            return c;

      }

      void Display( )

      { cout << "The sum is:" << c << "\n";}

};

int main()

{

      Test obj;

      obj.Addition(10,20);

      obj.Display();

      return 0;

}

Output

The sum is: 30

Example :1

Write a C++ program that inputs two numbers and outputs the largest number using class.

Solution:

/***********************************************

Program to check the largest number

************************************************/

#include<iostream>

using namespace std;

class Test

{

int a,b;

public:

void Get_num()

{

     cout << "Please two numbers: "<<endl;

      cin >>a>>b;

}

void Check_largest()

{

     if(a>b)

          cout<<a<<" is largest number"<<endl;

     else

          cout<<b<<" is largest number"<<endl;

}

};

int main()

{

     Test obj;

     obj.Get_num();

     obj.Check_largest();

     return 0;

}

Example :2

 Write a C++ program to check whether an integer is a prime or a composite number.

Solution :

 #include<iostream>

using namespace std;

class Test

{

int num;

public:

void Get_num()

{

     cout << "Please enter a positive integer" << endl;

      cin >> num;

}

void Check_prime()

{

int flag = 1;

for(int n = 2; n <= num ‒ 1; n++)

{

     if(num % n = = 0)

     {

          flag=0;

     }

}

if(flag= =1) 

     cout<<num<<" is a prime number"<<endl;

else

     cout<<num<<" is a composite number"<<endl;

}

};

int main()

{

     Test obj;

     obj.Get_num();

     obj.Check_prime();

     retrun 0;

}

Output(Run 1)

Please enter a positive integer

5

5 is a Prime number

Output(Run 2)

Please enter a positive integer

10

10 is a composite number

 

Example : 3

Consider a Bank Account class with Acc No and balance as data members. Write a C++ program to implement the member functions get_Account_Details() and display_Account_Details(). Also write suitable main function.

Solution:

/******************************************

Program to implement Bank Account class

*******************************************/

#include <iostream>

using namespace std;

class BankAccount

{

int AccNo;

double balance;

public:

void getAccDetails()

{

       cout<<"\n Enter the Account Number:

       cin>> AccNo;

       cout<<"\n Enter the Balance Amount:

       cin>>balance;

}

void DisplayAccDetails()

{

       cout<<"\nAccount Number: "<<AccNo;

       cout<<"\nBalance Amount: "<<balance;

        cout<<endl;

}

};

int main()

{

       BankAccount obj;

       obj.getAccDetails();

       cout<<"\n The account details are ..."<<endl;

       obj.DisplayAccDetails();

       return 0;

}

Output

Enter the Account Number: 101

Enter the Balance Amount: 10000

The account details are...

Account Number: 101

Balance Amount: 10000

 

2. Accessing Class Members that are Defined Outside the Class

•  The members functions that needs to be defined outside the class are defined using the scope resolution operator. Following program illustrates it.

/***************************************************************************

Program that uses a class where the member functions are defined outside a class

*********************************************************************/

#include <iostream>

using namespace std;

class Test

{

private:

 int a,b,c;

public:

       int Addition(int,int);

       void Display();

};

int Test::Addition(int a, int b) // Definition of function

{                                // Outside the class

       c= a+b;

       retum c;

}

void Test::Display()

{ cout << "The sum is:" <c< "\n";}

int main()

{

       Test obj;

       obj.Addition(10,20);

       obj.Display();

return 0;

}

Output

The sum is:30

3. Scope Resolution Operator

•  The :: operator is used to define the scope of the variable or function.

•  One can declare the function inside the class and can write its definition outside the class. But while doing so the programmer has to specify the belonging class name, scope operator and name of the function.

•  Let us discuss a C++ program which is making use of scope resolution operator.

C++ Program

#include<iostream>

using namespace std;

int a=5;

int main()

{

int a=15;

{

int a=20;

cout<<"INNER BLOCK\n";

cout<<"Value of a= "<<a<<endl;

cout<<"The scope of a= "<<::a<<endl;

{

int a=25;

cout<<"INNER‒INNER BLOCK\n";

cout<<"Value of a = "<<a<<endl;

cout<<"The scope of a= "<<::a<<endl;

}

}

cout<<"OUTER BLOCK\n";

cout<<"Value of a = "<<a<<endl;

cout<<"The scope of a= "<<::a<<endl;

 retum 0;

}

Output

INNER BLOCK

Value of a= 20

The scope of a= 5

INNER‒INNER BLOCK

Value of a= 25

The scope of a= 5

OUTER BLOCK

Value of a = 15

The scope of a= 5

Program Explanation

•  In above program we have redeclared a variable a whose value is modified on entering each new block. Note that a block can be defined using { and }.

•  The scope resolution operator is used to denote the scope of the variable. The scope of the variable is always a global scope. Hence each time we get output as 5 for :: a but the value of variable a gets changed each time in the block and that corresponding value can be displayed as an output.

 

Review Question

1. Explain in detail about class, objects, methods and messages.