A null pointer points to nothing or nowhere and is initialized to NULL or 0. Pointers must be initialized to NULL to indicate no memory is allocated yet. Functions returning pointers may need to indicate errors by returning a null pointer. Passing NULL to a function avoids passing an invalid memory address. Dereferencing a null pointer will cause a program to abort, so pointers should be checked against NULL before accessing their value.

2.  Pointer variable point to “nowhere” or “nothing”
 Not to an existing object
 Initialized with a value NULL or 0 regardless of the pointer type
 By default, C doesn’t initialize pointers to NULL
 By default, C doesn’t initialize pointers to NULL
int *p = 0;
int *p = NULL;
 Any pointer which is initialized to 0 or NULL is called a null pointer
 An uninitialized pointer is not a null pointer because it points “somewhere,”
syntax for
declaring a
NULL pointer

4.  Many functions that return a pointer also need
to indicate an error condition when it occurs
 To pass a null pointer to a function argument
when we don’t want to pass any valid memory
when we don’t want to pass any valid memory
address.
int fun(int *ptr)
{
//……
return 10;
}
fun(NULL);

5.  To check for null pointer before accessing any
pointer variable.
 Dereferencing a null pointer will abort a program
 To initialize a pointer variable when that pointer
 To initialize a pointer variable when that pointer
variable isn’t assigned any valid memory address yet.
int *p = NULL;
...
if (p != NULL)
printf(“%dn”, *p);
Initialize p to NULL
After processing ...
... check whether p is still null