pointer

A pointer is a variable which is used to store address of another variable. Whenever a variable declaration is done, it tells the compiler three things.

For eg., consider the following declaration:

int a=5;

It tells to

(i)                 Reserve space in memory to hold the integer value.

(ii)               Associate the name ‘a’ with this memory location

(iii)             Store the value 5 at this location.

The address of a variable can be printed using the operator ‘&’. This is known as ‘address of’ operator.

        

Eg.,

            void main( )

            {

            int a=5;

            printf(“address of %d is %u”, a, &a);

           }

Where the control string %u denotes to print an unsigned integer.

NOTE:-The ‘&’ operator can be used only with a simple variable or an array element. It cannot be used with constants, array names and expression.

Eg.,

            &45,

            &(a+b),

            int a[5]; &a are illegal.

Declaration of pointers:-

            Like normal variables, a pointer variable should also be declared before it is used. It can be done in the following form:

Syntax:-

            datatype *variablename;

Here, ‘*’ is known as ‘value at address’ operator or indirection operator.

Ø  It tells that the variable is a pointer variable.

Ø  Datatype indicates the datatype of the value which is stored in the address location indicated by the pointer variable.

Eg.,

            int *p;

It indicates that p is a variable, which stores the address of an integer value.

            float *q;

It indicates that q is a variable, which stores the address of a float value.

            char *r;

It indicates that r is a variable, which stores the address of a character value.

Initialization of pointers:-

            Assigning address of some variable to a pointer is known as pointer initialization.

Eg.,

            int  x,*pt;

                   pt=&x;

            void main( )

            {

            int *p,a=5;

            p=&a;

            pirntf(“%d is at addres %u”,a,p);

            }

Accessing values of variables:-

            The value of a variable can be accessed in two ways. One way is to refer to the variable through its name and other way is to refer through the address location.

Eg., prog:-

            void main( )

            {

            int a=5,*p;

            float b=2.5,*q;

            char c=’a’,*r;

            p=&a;

            q=&b;

            r=&c;

            printf(“a=%d, address of a=%u”,*p,p);

            printf(“b=%d, address of b=%u”,*q,q);

            printf(“c=%d, address of c=%u”,*r,r);

            }

NOTE: - Whatever may be the datatype at the declaration of pointer variable, it takes 2 bytes of memory since the value of pointer variable is always an unsigned integer.

Ø  A Program to perform arithmetic operations using pointers.

Ø   

#include<stdio.h>

#include<conio.h>

void main( )

{

        int a,b,*p1,*p2;

        p1=&a;

        p2=&b;

printf(“enter any two values”);

scanf(“%d%d”,&a,&b);

printf(“addition=%d”,(*p1+*p2);

printf(“subtraction=%d”,(*p1+*p2);

printf(“product=%d”,(*p1+*p2);

printf(“division=%d”,(*p1+*p2);

getch( );

 }