STATIC DATA MEMBERS & CONSTANT MEMBER FUNCTIOS in C++

STATIC DATA MEMBERS & CONSTANT MEMBER FUNCTIONS

Static data members

static data member is a data member that is shared by all the objects of a class.Only one copy of static data member is kept in memory

By this example your idea will be clear about static data members

static data members

#include <iostream>

using namespace std;

class alpha

{

private:

            int id;

            static int count;

public:

            alpha()

            {

                        count++;

                        id=count;

            }

            void print()

            {

                        cout<<"My id is"<<id;

                        cout<<"count is"<<count;

            }

};

int alpha ::count=0;   //definition of count

void main ()

{

            alpha a1,a2,a3;

                        a1.print();

            a2.print();

            a3.print();

}

This example will clear your idea . This simple ,easy and awesome  space for beginners

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Constant data members

If you dont want to change data members then keyword const is used.

This example demonstrates const member functions

class aclass

{

private:

           int alpha;

public:

           void nonFunc()                  // non const member function

{

alpha=100;                           //ok

}

void conFunc() const                  // constant member function

{

            alpha=100;                 // error , cannot modify a member

}

};

This example surely help you in  understanding of const member function

This is a completely solved example.

#include <iostream>

using namespace std;

class rational

{

private:

            int num;

            int dnum;

public:

            rational():num(1),dnum(1)

            {}

            void get ()

            {

                        cout<<"enter numerator";

                        cin>>num;

                        cout<<"enter denomenator";

                        cin>>dnum;

            }

            void print ()  const      // const keyword is used

            {

                        cout<<num<<"/"<<dnum<<endl;

            }

            void multi(rational r1,rational r2)

            {

                        num=r1.num*r2.num;

                        dnum=r1.dnum*r2.dnum;

            }

};

void main ()

{

            rational r1,r2,r3;

            r1.get();

            r2.get();

            r3.multi(r1,r2);

            r3.print();

           

}

For practice you should solve one more programming example like distance class. Practice makes a man perfect

POINTERS in C++

Pointers

A variable that holds an address value is called a pointer variable or simply pointer.Pointers are hobgoblin of c++ programming.

What are pointers for ?          Here some common uses are

·                     Accessing array elements.

·                     Passing arguments to a function when the function needs to modify the origonal argument.

·                     Passing arrays and strings to function.

·                     Obtaining memory from the system.

·                     Creating data structures such as linked lists.

Pointers are important feature of c++ programming. But many other languages such as java , visual Basics have no pointers. You can do a  lot of programming without pointers but pointers are assentials for c++ programming language.

The idea behind pointers is not complicated.Every byte in computer memory has an address.Addresses are  numbers,just as for houses on a street.

The address of operator &:

Address occupied by a variable using the address operator &. Here is a short example that will help you in understanding that topic.

#include <iostream>

using namespace std;

int main ( )

{

int var1 = 10;

int var2 = 20;

cout << &var1<<endl;

cout << &var2<<endl;

return 0;

}

Run this program on your system and machine and then see what the address of var1 and var2 .

Address is not the value of var1 which is 10. Address would be in the form of 6to7 digits.

Address by pointer variables:

By the address we can find where things in memory.

What is the data type of pointer variable ?

A pointer to int  ,is not type int .You might think a pointer data type would be called something like pointer or p or ptr.

Example of pointer ( address variables )

#include <iostream>

using namespace std;

int main ( )

{

int var1 = 10;

int var2 = 20;

cout << &var1<<endl;

cout << &var2<<endl;

int *ptr ;

ptr = &var1 ;

cout <<ptr ;

ptr = &var2 ;

cout<< ptr;

return 0;

}

Sample run can be shown when you run this program on your system.

Pointers must have a value:

An address like 0*8ffff4ff can be thought of as a pointer constant.

When we first define a variable , it holds no value. It may hold a garbage value.But in case of pointers , a garbage value is the address of something in memory. So before a pointer is used   ,  a specific address must be placed in it.

ptr = &var;