Effetive Use of Pointers

Abstact :

     This article shows an impotance of pointers. pointer is nothing but variables which can hold address. pointer variable need memory address as its value. we can't stotre direct value in pointer variables. Understanding pointer has  litle confusion to beginers but there's no real magic to pointers, and a lot of readers will already be familiar with their use. The only peculiarity of C is how heavily it relies on the use of pointers, compared with other languages, and the relatively permissive view of what you can do with them.

Declaring pointers

Pointer is a variable so  just like other variables, you have to declare pointers before you can use them. Pointer declarations look much like other declarations: but don't be misled. When pointers are declared, the keyword at the beginning (c int, char and so on) declares the type of variable that the pointer will point to. The pointer itself is not of that type, it is of type pointer to that type. A given pointer only points to one particular type, not to all possible types. Here's the declaration of an array and a pointer:

  example:

      int *p, *name, *ptr;

      int x, *pt;    // Declare with other variables also.

Once pointer has been declared we must initialize pointer variable before use.

      p = &x;

     pt= name;  //  name is array variable of type char

                     //  all array variable name can directly assign to pointer variables

Example for array : int ar[5], *ip; ip = &ar[3];

In that example, the pointer is made to point to the member of the array ar whose index is 3, i.e. the fourth member. This is important. You can assign values to pointers just like ordinary variables; the difference is simply in what the value means. The values of the variables that we have now are shown in Figure  (?? means uninitialized).

      ar[0]    ar[1]   ar[2]

the avove three array variables can have continious memory locations.  these variables can initialized indiviualy or by single statement like this.

     ar[0] = &x;    ar[1]= &y;  ar[2]=&z;

      or

   ptr=ar;    // normal initializtion

   Example program.

#include
#include
main(){
      int x, *p;

      p = &x;         /* initialise pointer */
      *p = 0;         /* set x to zero */
      printf("x is %dn", x);
      printf("*p is %dn", *p);

      *p += 1;        /* increment what p points to */
      printf("x is %dn", x);

      (*p)++;         /* increment what p points to */
      printf("x is %dn", x);

      exit(EXIT_SUCCESS);
}