Pointer

POINTER:

Pointer is the special variable to find out another variable. OR also we can say the variable that hold memory addresses are called pointers. Thus pointer is a variable that contains an address which is a location of another variable in memory.

To store the address of a variable we have to use the operator “&” called as the address operator.

Ex.:

float *x;           // x is a float pointer

int *p;              // p is a integer type pointer

int price=420;

p = &price;

 printf(“%d”,price);          420

printf(“%u”,&price);        2024

printf(“%u”,p);               2024

printf(“%u”,&p);            2088

printf(“%d”,*p);             420

printf(“%d”,*(&price));    420

      price       p

      420        2024

      2024      2088

Rules for the declaring pointer variable:-

1.  The * symbol(asterisk) is used before variable name at the time of declaring. It indicates a pointer variable.

2.  A pointer memory allocation it only accepts or stored the memory address of another variable.

3.  Which types of memory you want to point out you need to declared that type pointer variable.

Address Operation :

-  The address of a variable can be represented by combining ‘&’(Ampersand) with a pointer variable.

-  Since the actual location of a variable depends on the system to get the address of an integer variable

-  E.g.      y=&x;

assigns the address of x to y where y is a pointer. The variable y points to x.

POINTER TO POINTER:

-   It is possible to make a pointer to point to another pointer

-   It is known as pointer to pointer

-   A variable that is a pointer to a pointer must be declared as

   int **p;

-   This declaration tells the compiler that p is a pointer to a pointer of int type.

-   The pointer p is not pointer to an integer, but rather a pointer to an integer pointer.

-   E.g.

int x, *p1, *p2;

x=5;

p1=&x;

p2=&p1;

Variable       ---   x --   P1  --  P2

Contents value  5---1002--5001

Variable Address----1002---5001

                                    -----7002

P2 à p1à x

POINTER WITH ARRAY:

A pointer can be used to point the first element of the array. This address can be then passed to a function. This address can be then used in the function to access all the elements of the array.

Q. Write a program to demonstration of pointers to the array.

#include<stdio.h>

#include<conio.h>

void main()

{

      int a[5]={10,20,30,40,50};

      int *p;             // pointer variable

      p=&a[0];        // assign memory address of a variable

          printf("\nAddress of a=%u",p);

          printf("\nValue of a=%d",*p);

      p=&a[1];        // assign memory address of a variable

          printf("\n\nAddress of a=%u",p);

          printf("\nValue of a=%d",*p);

     

      p=&a[2];        // assign memory address of a variable

          printf("\n\nAddress of a=%u",p);

          printf("\nValue of a=%d",*p);

      p=&a[3];        // assign memory address of a variable

          printf("\n\nAddress of a=%u",p);

          printf("\nValue of a=%d",*p);

      p=&a[4];        // assign memory address of a variable

          printf("\n\nAddress of a=%u",p);

          printf("\nValue of a=%d",*p);

getch();

}

 

POINTER in a STRUCTURE:

A structure is a user defined data type and has many elements. These elements can be accessed using the variable name and dot operator. A pointer can be declared for a structure. The elements of a structure can be accessed using pointer by the (->) arrow operator.

E.g.

struct book

{

    int pages;

    float price;

} b1, *ptr ;

ptr=&b1;

printf(“%d”,ptr->pages);

printf(“%d”,ptr->price);