Pointer in C Program

Pointer

Pointer is a variable that stores the address of another variable. They can make some things much easier, help improve your program's efficiency, and even allow you to handle unlimited amounts of data.

C Pointer is used to allocate memory dynamically i.e. at run time. The variable might be any of the data type such as int, float, char, double, short etc.

Syntax : Pointers require a bit of new syntax because when you have a pointer, you need the ability to both request the memory location it stores and the value stored at that memory location.

data_type *ptr_name;

Example :

int *a; char *a;

Where, * is used to denote that ''a'' is pointer variable and not a normal variable.

Key points to remember about pointers in C:

# Normal variable stores the value whereas pointer variable stores the address of the variable.

# The content of the C pointer always be a whole number i.e. address.

# Always C pointer is initialized to null, i.e. int *p = null.

# The value of null pointer is 0.

# & symbol is used to get the address of the variable.

# * symbol is used to get the value of the variable that the pointer is pointing to.

# If pointer is assigned to NULL, it means it is pointing to nothing.

# Two pointers can be subtracted to know how many elements are available between these two pointers.

# But, Pointer addition, multiplication, division are not allowed.

# The size of any pointer is 2 byte (for 16 bit compiler).

Example program for pointer in C:

#include

int main()

{

int *ptr, q;

  q = 50;

  /* address of q is assigned to ptr */

  ptr = &q;

  /* display q's value using ptr variable */

  printf("%d", *ptr);

  return 0;

}

NULL Pointers

It is always a good practice to assign a NULL value to a pointer variable in case you do not have 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. Eg : int *ptr = NULL;

The value of ptr is 0

Pointer Arithmetic

As you understood pointer is an address which is a numeric value; therefore, you can perform arithmetic operations on a pointer just as you can a numeric value. There are four arithmetic operators that can be used on pointers: ++, --, +, and -.

Example :

ptr++;

ptr--;

ptr+21;

ptr-10;

If a char pointer pointing to address 100 is incremented (ptr++) then it will point to memory address 101

Pointers vs Arrays

Pointers and arrays are strongly related. In fact, pointers and arrays are interchangeable in many cases. For example, a pointer that points to the beginning of an array can access that array by using either pointer arithmetic or array-style indexing.

int main ()

{

int var[3] = {1, 2, 3};

int *ptr;

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

ptr++;

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

return 0;

}

this code will return :

1

2

Pointer to Pointer

A pointer to a pointer is a form of multiple indirection or a chain of pointers. Normally, a pointer contains the address of a variable. When we define a pointer to a pointer, the first pointer contains the address of the second pointer, which points to the location that contains the actual value. int main ()

{

int var;

int *ptr;

int **pptr;

var = 3000;

ptr = &var;

pptr = &ptr;

printf("Value of var :%d \n", var);

printf("Value available at *ptr :%d \n",*ptr);

printf("Value available at **pptr :%d\n",**pptr);

return 0;

}

this code will return

Value of var :3000

Value available at *ptr :3000

Value available at **pptr :3000