#include <stdio.h>

int  main (void)
{
	/* a,b,e  are declared as integers.  However, c and d  are  
		pointers to integers - notice star before identifiers.
	    This demonstrates the 1st usage of "*" - declaring a pointer variable */
	int a, b, *c, *d, e;

	a = 10;
	/* Below, "star" is used simply as multiplication */
	b = a * 4;
	c = &a; /* address of a goes into c, i.e. c points to 10 */
	d = &b; /* address of b goes into d, i.e. d points to 40 */

	/* Next line is using "star" to retrieve the value of the variable
		pointed by the pointer. This is the 2nd usage of  "*" - dereference */
	e = *c + *d; /* Value of *c is a and value of *d is b.Therefore, e=10+40=50.*/

	/* The 1st format string matches the 1st value to be printed, 
		the 2nd format string matches the 2nd value, and so on ... */
	printf ("a= %d, b= %d, *c= %d  *d= %d  e=*c+*d=%d\n", a, b, *c, *d, e);

	*d = a;	/* value pointed by d is assigned a, i.e. *d becomes 10. But d
           holds the address of b. As a _side-effect_, value of b changes too ! */

	printf ("a= %d, b=*d=%d, *c= %d  *d=a=%d  e= %d \n", a, b,*c,*d,e);

	d = &a; /* d no longer points to b, but now it points to a. However, 
		nothing else changes, just direction of pointer d changed.*/

	printf ("a= %d, b= %d, *c= %d  *d= %d  e= %d \n", a, b,*c,*d,e);

	/* Operation (a % b) produces remainder from dividing a=10 by b=10, i.e., 0*/

	*c = *d - a % b + *c;  /* We change the value pointed at by c, but
	since c is a pointer to a, and d was also assigned to point to a,
	as a side-effect, we also change both a and the value pointed by d.*/

	printf ("Do you understand why\n");
	printf ("a= %d, b= %d, *c= %d  *d= %d  e= %d ?\n", a, b,*c,*d,e);

	return (0);
}

/* Output:

a= 10, b= 40, *c= 10  *d= 40  e=*c+*d=50
a= 10, b=*d=10, *c= 10  *d=a=10  e= 50 
a= 10, b= 10, *c= 10  *d= 10  e= 50 
Do you understand why
a= 20, b= 10, *c= 20  *d= 20  e= 50 ?

*/