Pointer

consider this declaration
int i=3;
these declaration tells to compiler to;

Reserve space in memory to hold the intiger value.
Associate the name i with this memory location .

store the value b at this location.

                  i-> location name
	        [3]->value at location
              65525->location number (address)

Program to print address of variable :

        void main()
          {
	    int i=3;
	    printf(""\n address of i=%u",&i);
	     printf("\n value of i=%d",i);
	  }
  
    Output : address of i=65525
             value of i=3

In above program and the address of operator .The expression and i returns the address of variable which is in this case happens to be 65525 since 65525 represent an address there is no question of a sign being associated with it hence it is printed out %u which is a format specifier for printing an unsigned integer . we have been using the '&' operator all the time in the scanf()statement.

Defination :

Pointer is a variable which stores the address of another variable rather than value.

We can not use pointer without declaring it.

         It is declared as 
           
          int *j;
	  int i=3;
	  int *j;
	  j=&i;
  
    j as an pointer here which is pointing to the address of variable  i.
    datatype of i and j should be the same.

Program-

       void main()
	{
   	   int i=3;
	   int *j;
	   j=&i;
             printf("\n address of i=%u",&i);
             printf("\n address of j=%u",&j);
             printf("\n value of i=%d",i);
             printf("\n value of j=%u",j);
             printf("\n value of i=%d",*(&i));
         }

         Output :
              address of i=65524
               address of j=65522
	       value of i=3
	      value of j=65524
               value of i=3

Functions of pointer-

There are two types of functions call:

Call by value->Sending the value of argument.
Call by reference->Sending the address of arguments.

Swapping of two numbers with call by value:

       void swap(int,int);
	void main()
         {
            int a=10,b=20;
            swap(a,b);
            printf("before swapping");           //before swapping
            printf("\n a=%d b=%d"a,b);
         }
         void swap(int x,int y)
          {
             int t;
              t=x;
               x=y;              //swapping of number using third variable
              y=t;
             printf("after swapping");
             printf("\n x=%d y=%d",x,y);
          }


    Output :
             before swapping
             a=10   b=20

              after swapping
              x=20    y=10

Swapping of two numbers with call by reference

        void swap(int *x,int *y)
         void main()
           {
              int a=10,b=20;
              swap(&a,&b);
              printf("before swapping");
              printf("\n a=%d b=%d"a,b);
           }

             void swap(int *x,int *y)
             {
                int t;
                t= *x;
                *x=*y;
                *y=t;
                printf("after swapping");
                printf("\n x=%d y=%d",x,y);
             }

       Output :
                before swapping
                a=10   b=20

                 after swapping
                x=20    y=10

NOTE:

If we want that value of actual argument should not get changed in function begin called then pass the actual argument by reference.
If we want that value of actual argument should get changed in the function beign called then pass actual argument by reference.
If a function is to be made to return more than one value at a time ,then return these values indirectly by using call by reference.