Pointers in C

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What is pointer in C?

A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before using it to store any variable address.

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Why we use pointers?

pointers are used to create dynamic data structures -- data structures built up from blocks of memory allocated from the heap at run-time.pointers are also used to handle variable parameters passed to functions. Pointers provides an alternative way to access information stored in array

How to Use Pointers?

There are a few important operations, which we will do with the help of pointers very frequently. (a) We define a pointer variable, (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand.

NULL Pointers

It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A pointer that is assigned NULL is called a null pointer.

Sr.No.	Concept & Description
1	Pointer arithmetic There are four arithmetic operators that can be used in pointers: ++, --, +, -
2	Array of pointers You can define arrays to hold a number of pointers.
3	Pointer to pointer C allows you to have pointer on a pointer and so on.
4	Passing pointers to functions in C Passing an argument by reference or by address enable the passed argument to be changed in the calling function by the called function.
5	Return pointer from functions in C C allows a function to return a pointer to the local variable, static variable, and dynamically allocated memory as well.

Example of pointers:-

#include<stdio.h>

int main()

{

int i,a[4]={10,20,30,40};

int *p;

p=a;

for(i=0;i<4;i++){

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

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

 p++;

}

}

Null pointer:-

#include <stdio.h>

int main () {

   int  *ptr = NULL;

   printf("The value of ptr is : %x\n", ptr  );

   return 0;

}

Pointer In 2d array:-

#include<stdio.h>

  

int main()

{

  int arr[2][3] = {

                    { 10, 11, 12 },

                    { 20, 21, 22 }

                  };

  int i, j;

  for (i = 0; i < 2; i++)

  {

    printf("Address of %dth array = %p %p\n",  

                    i, arr[i], *(arr + i));

      

    for (j = 0; j < 3; j++)

      printf("%d %d ", arr[i][j], *(*(arr + i) + j));

    printf("\n");

  }

  

  return 0;

}

Note::-

If there any pointer is placed in the front of  function eg:- int *pte() then it is called as self refrrential pointer