POINTER

 Pointer

Pointer is a special type of variable, which is used to store the address of another variable. This variable starts with asterisk symbol (*). The pointer can use two special operators.

1.The first one is *(asterisk), it is called indirection operator or value of operator.

2.The second is &(ampersand), it is called address of operator. 

int  *ip;       //ip is our integer pointer

int a, *ip; a=5; ip=&a; /*here we can assign the address of variable a to pointer variable ip*/

Pointer declaration

A pointer is declared same as a variable with a specific data type. But declared with an asterisk sign.

As show in the example below:

Example

float *fp;                            //fp is our Float pointer

 char *cp;                          //cp is our character pointer

Address operator & (Ampersand)

As mentioned above, pointer uses two special operators; one of them is the address operator, which is used to assign the address of the variable to the pointer variable.

 As shown the example below:

int a,*ip;
a=5;
ip=&a;

 Indirection operator *(asterisk)

Indirection operator is also known as value of operator, which is used to print the value of the variable through pointer variable.The indirection operator is used to declare a pointer.

As shown in the example below:

int  a, *b;
a=5;
b=&a;
printf("\n the value of a=%d",a);
printf("\n the value through pointer=%d",*b);/* here b print the value of a*/

#include<stdio.h>

#include<conio.h>

void main()

{

int a,*b;

clrscr();

a=5;

b=&a;

            printf("\n the value of a %d",a);

            printf("\n the address of a=%u",&a);

            printf("\n the value of b=%u”,b);

            printf("\n the value of b through pointer =%d",*b);

            getch();

}

output

the value of a=5

the address of a=65524

 the value of b=65524

the value through pointer b=5

Write a program to add two numbers using pointers.

#Include<stdio.h>

 #include<conio.h>

void main()

{        

         int a,b,*c,*d, e; 
         clrscr();

         printf("enter the value of a=");

 scanf("%d",&a);

printf("enter the value of b=");

scanf("%d",&b);

c=&a;

d=&b;

e=*c+*d;

printf("sum=%d",e);

getch();

}

Write a program to swap two numbers using pointer without using third variable.

#Include<stdio.h>

 #include<conio.h>

void main()

{

int a, b, *c, *d;

clrscr();

printf("enter the value of a=");

scanf("%d", &a);

printf("enter the value of b=");

scanf("%d", &b);

c=&a;

d=&b:

//swapping of two numbers

*c=*c+*d;

 *d= *c- *d;

 *c=*c-*d;

printf("\after swapping the numbers");

printf("\n now the value of a=%d", a);

 printf("\n now the value of b=%d",b);

 getch();

}

Arithmetic pointers

We can also use pointers forarithmetic purposes same as variables. When we write a++ it increase the value of the variable but when we write p++, it is a pointer variable it moves the pointer to the next memory location. to the next location is 65527. Note that we can perform any arithmetic operation on a pointer variable accessed with the help of pointer. Normally we can assign the address of first

element of an array to the pointer. When we increment inside the pointer, it increments its address. It means it reads the address of next element. The address of first element of an array is called base address of array mention the index of the array.

Like

int *p;

p++;

or

p=p+3;

Assume that the address of p is 65524.

When we add 3 to the pointer it move

Pointers with array

The values of the array can be

As shown in the example below:

int a[]=[2,4,3,5,6];

int *ip;

 //here we can assign the address of array to the pointer.

ip=&a[0]; /*We can also assign the address of the first element to the pointer*/

ip=a;//Here we need not to

 Write a program to find the maximum number from the given array-using pointer.

#include <stdio.h>

#include <conio.h>

void main()

{        

          int a[5],*p,i,b;

clrscr();

for(i=0;i<5;i++)

{

          printf(“enter any number”);

          scanf(“%d”,&a[i]);

}

p=&a[0];

b=a[0];

for(i=0;i<5;i++)

{

          if(*p>b)

          {

                    b=*p;

}

p++;

}

printf(“the maximum number =%d”,b);

getch();

}

Pointer With String

A String is a group of characters, which contain characters. We can access the string using that read one character at time. We can assign the address of first element of character array to the pointer.

Write a program to print your name-using pointer.

#include <stdio.h>

#include <conio.h>

void main()

{        

          char a[50]=”hari”;

          char *p;

          clrscr();

          p=a;

          while(*p!=’\0’)

          {

                    printf(“%c”,*p);

                    p++;

}

getch();

}
Output:-
hari

Pointer with two Dimensional array

We can also access the two dimensional array using pointer in which we can declare array with pointer.

#include <stdio.h>

#include <conio.h>

void main()

{        

          int a[2][2],*p,i,j;

for(i=0;i<2;i++)

{

for(j=0;j<2;j++)

{

printf("\nenter any number");

 scanf("%d",&a[i][j]);//11 26 39 43

}

          }

p=&a[0][0];

for(i=0;i<2;i++)

{

for(j=0;j<2;j++)

{

printf("%d", *p);

                        p++;
                }

printf("\n");

          }

getch();

}
Output:-
11 26
39 43

Pointer with structure

We can also access the elements of the structure with help of pointer. We can assign the address of the structure variable to the pointer variable. For accessing the elements we can use arrow (->) operator in place of dot(.) operator. Write a program to access the elements of the structure-using pointer.

#include<stdio.h>

#include<conio.h>

struct  stu

{

char name[20];

int roll;

};

void main()

{

struct stu s={"harsh”,1};

struct stu *p;

 clrscr();

 p=&s;

printf("\n your name=%s" ,p->name);

printf("\n your roll= %d",p->roll);

 getch();

}

Pointer to Pointer

Pointer to Pointer means which can store the address of another pointer variable. A pointer-to-pointer variable start with double asterisk (**) sign. A simple pointer can store the address of a variable but a pointer to pointer can store the address of another pointer.

 As shown in the example below:

Example:

Int  a, *p,**pp;

a=5;

p=&a;

pp=&p;

 Example program

#include<stdio.h>

#include<conio.h>

vold main()

{

int a,*p,**pp;

clscr();

 a=5;

 p=&a;

 pp=&p;

 printf("\nthe value of a=%d",a);

 printf("\nthe value of pointer = %d", *p);

printf("\n the value of painter to pointer=%d”,**pp);

           getch();
}

Output:- 
the value of a=5
the value of pointer =5

the value of painter to pointer=5

Pointer passing as argument to the Function

We can also pass pointer variable as an argument into the function. This is also known as reference variables.

As shown in the example below:

#include<stdio.h>

#include<conio.h>

 void swap(int *a, int *b);

 void main()

{

int x,y;

 clrscr();

 printf("enter the value of x");

 scanf("%d",&x);

 printf("\nenter the value of y");

scanf("%d",&y);

printf ("\nbefore swapping”);

 printf(“\nx= %d y=%d",x,y);

 swap(&x,&y);

 printf("\n after swapping ");

 printf("\n the value of x=%d",x);

 printf("\n the value of y= %d",y);

getch();

 }

void swap(int *a, int *b)

{

            *a=*a+*b;

            *b=*a-*b;

            *a=*a-*b;

}

Output :-
enter the value of x 5
enter the value of y 9
before swapping
x=5 y=9
after swapping
 the value of x=9
 the value of y=5

Function Returning Pointer

A function can return a pointer same as it returns a variable. In this we can declare and define the function with indirection (value of operator) operator.

As shown in the example given below

# Include<stdio.h>

 #include<conio.h>

int *show();

 int *show()

{

int a;

printf("enter any number");

scanf("%d", &a);

a=a*a;

return &a;

}

void main()

{

int *p;

clrscr();

p=show();

printf("\n The value of a=%d", *p);

getch();

}

Output:-
 enter any number 5
 The value of a= 25

Advantages of Pointers

1. Pointers increase the speed of the program.

2. It is used to read the address of the variable.

3. It is used to the manage memory efficiently.

4. For Dynamic memory allocation we can use pointers.

5. With the help of pointers we can create efficient programs.

6. Pointers can be used to access elements of the structure.

7. It can pass as arguments into the function.

Difference Between A Variable And Pointer Variable

Variable	Pointer Variable
A variable starts with an alphabet.	A pointer variable starts with asterisk sign.
It can store the value.	It can store the address of another variable
It can not use any special operator.	It uses two special operators first is address operator (&)and second is indirection operator(value of operator)(*).
When we perform any arithmetic any arithmetic operation on variable it increases the value of the variable. Like int a=5; a++; Now value of a=6;	when we perform operation on pointer variable it moves to the next memory address. It increments in their address.  Like int a=5,*p;  p=&a; p++; Now it increment in their address
A float variable can store the value of an integer variable	float pointer can store the address of a float variable it cannot store the address of Integer variable.
Example int a; a=5;	Example int *p,b=5;  p=&b;

It is also known as pointer variation. It mean the slightly difference between the pointer variable and other variable

Dynamic memory allocation

 Dynamic memory means, memory which is allocated at run time in place of compile time. In normal array or variable, the memory is allocated at compile time. It is known as static memory. The memory which is allocated at run time is known as dynamic memory. This memory is accessed using pointer. For dynamic memory we can use various methods, which are stored in the alloc.h header file.

These function are:

1. malloc() function

2. calloc() function

3. realloc() function

4. free() function

1.     malloc()Function:- malloc means memory allocation function. This function is used to allocate dynamic memory at run time to the pointer variable. This function allocates a single block of memory of specific data type.

As shown in the example below:

Write a program to print the elements of pointer using malloc function

 #include<stdio.h>

#indude<conio.h>

 #include<alloc.h>

 void main()

{

int i, n,*p;

clrscr();

printf("enter the size of the values");

 scanf("%d",&n);

 p=(int*)malloc(n);

for(i=0;i<n;i++)

{

printf("enter any number);

 scanf("%d",(p+i));

            }

for(i=0;i<n;i++)

{

printf("%d\n",(*p));

p++;

}

getch();

}

2.     Calloc() Function:- This function is also used for dynamic memory allocation same as malloc function but this function contain two arguments. The first argument tells the number of elements(items) and the second argument tells their size. It allocates number of blocks memory. As shown in the syntax and example program given below:

void calloc(number of Items, size);

#include<stdio.h>

#include<conio.h>

#include<alloc.h>

void main()

{

char *p=NULL; 

clrscr();

*p=(char*) calloc(10,sizeof(char));

 printf("enter any string “);

scanf("%s",p);

printf("%s",p);

 getch();

}

3.      Realloc() Function:- Realloc function means reallocation of memory. This function is used to reallocate memory to the preallocated pointer variable. This function is used to increase and decrease the size of the memory.

As shown in the syntax and example below:

#include <stdio.h>

#include <alloc.h>

#include <string.h>

 #include<conio.h>

void main()

{

char *p;

 clrscr();

 p = (char*) malloc(10);

strcpy (p, "Hari");

printf("String is %s",p);

 printf("\n Address is %u",p);

p = (char*) realloc(p,20);

 strcpy(p, "hari kapil");

 printf("String is %s",p);

 printf("\n New address is %u",p);
free(p);

 getch();

}

4.       Free function:- This function is used to release the memory which is occupied by the variable. That memory, which is allocated by the above discussed functions like malloc(), calloc(), realloc(). so this function is used to free the memory. This function contains a single argument, whose memory we want to release. As shown in the syntax and example below:

void free (pointer variable);

 Example free(p);