Pointers in C programming

            A pointer is a variable that stores a memory address of a variable. Pointer can have any name that is legal for other variable and it is declared in the same fashion like other variables but is always preceded by ‘ *’ ( asterisk) operator.

Applications of a pointer:

     There are a number of reasons for using pointers. Some of them are:

1)      Pointers can be used to pass information back and forth between a function and its reference point.

2)      Pointers provide a way to return multiple data items from a function via function arguments.

3)      Pointers provide an alternative way to access individual array elements. 

4)      They increase the execution speed as they refer address.

Pointer declaration

   Pointer variables can be declared as follows:

            Syntax:

                   data-type  *  variable_name;

            Examples:

               int *x; float *f; char *y;

  

          In the first statement, ‘x’ is an integer pointer and it tells to the compiler that it holds the address of any integer variable. In the same way ‘f’ is a float pointer which stores the address of any float variable and ‘y’ is a character pointer that stores the address of any character variable.

                Here * is called pointer or indirection operator. Normal variable provides direct access to their own values whereas a pointer provides indirect access to the values of the variable whose address it stores. The indirection operator (*) is used in two distinct ways with pointers, declaration and dereference. When the pointer is declared, the star indicates that it is a pointer, not a normal variable. When the pointer is dereferenced, the indirection operator indicates that the value at that memory location stored in the pointer is to be accessed rather than the address itself. Also note that * is the same operator that can be used as the multiplication operator. The compiler knows which operator to call, based on the context. An example

     void main( )

           {

      int v=10, *p; // Here, * indicates p as pointer

      p=&v;

      printf(“\n address of v=%u”,p);

      printf(“\n value of v=%d”,*p); // Here, * indicates value at address pointed by p

      printf(“\n address of p=%u”,&p);

       }

Output:

address of v=65524

 value of v=10

 address of p=65522

It can be illustrated as

                 Here v is an integer variable and its value is 10. The variable p is declared as pointer variable. The statement p=&v assigns address of ‘v’ to ‘p’ i.e. ‘p’ is the pointer to variable ‘v’. To access the address and value of ‘v’ pointer ‘p’ can be used. The value of ‘p’ is nothing but address of the variable ‘v’. To display the value stored at that location *p is used. The address of the pointer variable can be accessed using ‘&’ operator. Pointer variable can also be initialized at the time of declaration. It is done as follw.

           int a;

           int *p=&a;