/*
	                 PROCESS FORKING 		

  This program illustrates the fork() system call.

*/

#include <stdio.h>
#include <sys/ipc.h>  

main()
{
	int i ;
	int x = 10 ;
	int pid1, pid2, status ;

	printf("Before forking, the value of x is %d\n", x);

	/*
	   After forking, we make the parent and its two children
           increment x in different ways to illustrate that they
	   have different copies of x
	*/
	if ((pid1 = fork()) == 0) {

		/* First child process */
		for (i=0 ; i < 5; i++) {
		   printf("\t\t\t At first child: x= %d\n", x);
		   x= x+10;
		   sleep(1) ; /* Sleep for 1 second */
		}
	}
	else {

		/* Parent process */

		/* Create another child process */
		if ((pid2 = fork()) == 0) {

		    /* Second child process */
                    for (i=0 ; i < 5; i++) {
                   	printf("\t\t\t\t\t\t At second child: x= %d\n", x);
                   	x= x+20;
			sleep(1) ; /* Sleep for 1 second */
                    }
		}
		else {

			/* Parent process */
			for (i=0 ; i < 5; i++) {
		  	 	printf("At parent: x= %d\n", x);
		   		x= x+5;
				sleep(1) ; /* Sleep for 1 second */
			}

			/* 
			    The waitpid() system call causes the parent
			    to wait for a child process with a specific pid to complete
			    its execution. The input parameter can
			    specify the PID of the child process for
			    which it has to wait.
			*/

			waitpid(pid1, &status, 0);
			waitpid(pid2, &status, 0);
		}
	}
}