Pointers in C Language

Introduction

Pointers are a part of the C language and make the C language more powerful. The following arre some features ot them:

• A pointer mainly represents a data structure.
• It changes values of an actual argument passed to the function (“call by reference”).
• It is also for working with memory allocation dynamically.
• It is efficiently used with integer arrays and character arrays.
• A pointer always stores a memory address, not data values.
• A pointer holds the value aa an address.

Declaration

A pointer variable must be declared before use. The syntax for a pointer declaration is as follows.

Int *a;
Double *b;

Now a is a “pointer to an integer”and b is a “pointer to a double”.

The prefix * defines the variable as a pointer.

Example

Int *a;
Int b;
a=&b;

Here a contains the memory address of the variable b.

Arithmetic operation are limited to the following for pointers:

1. Integers and pointers can be added and subtracted.
2. Incremented and decremented
3. In addition, pointers can be assigned to each other

Example

Int *a,*b;
a=a+5;
b=a;

Call by Reference

Using call by reference means that a parameter is sent to the function in the form of an address location.

#include<stdio.h>
Void swap(int *p , int *q);
main()
{
   Int i=3,j=5;
   swap( &I , &j ); //sentind address of I and j variables
   printf("After swap, i=%d j=%d\n" ,I ,j );
   getch();
   return 0;
}
Void swap(int *p, int *q)
{
   Int temp;
   temp=*p;
   *p=*q;
   *q=temp;
}

Output

After swap, I=5 j=3

Pointers and arrays

A pointer always contains the base address of the memory location that makes up an entire array.

Declaration

Scanf(“%s” ,name);

Example

1. Int a[5];
2. a[5]=10;
3. *(a+5)=56;

All of those are the same thing.

Examples

1. Int a[100] , I , *p , sum=0;
   for (i=0 ; i<100 ;++I )
   Sum += a[i];

2. int a[100] , I , *p , sum=0;
   for (i=0 ; i<100 ; ++I )
   Sum += *( a + I );

3. int a[100] , I , *p , sum=0;
   for ( p=a ; p<&a[100] ; ++p )
   sum += *p;

   The following shows an array as function arguments:
   

   double sum(double *dp , int n )
   {
      Int I ;
      Double res=0.0 ;
      for ( i=0 ; i<n ; ++I )
      res += *( dp + I ) ;
      return res;
   }

That function needs a starting address in the array and the number of elements to be summed together.

Pointers and Character Strings

#include<stdio.h>
main()
{
   Char *cp ;
   cp = "Neeraj Kumar";
   printf("%c\n" , *cp );
   printf("%c\n" , *( cp + 7 ));
   return 0;
}

Output

N
K

We can use pointers to work with character strings. The value of the string constant address is the base address of the character array.

Thank you.