#include	<stdio.h>
#include	<stdlib.h>
#include	<unistd.h>
#include	<fcntl.h>
#include	<string.h>

main(int argc, char * argv [ ] )
{ int i, init = 0, prom, step1 = 1, step2 = 2;
  int fd; char buf [ 30 ];

	if ( ( fd = open (argv[1], O_CREAT|O_RDWR,0666 ) ) == -1 )
	{write(2,"Cannot open: file \n",20); exit(1); }
	write( fd, &init, sizeof (int) ) ;
	close(fd);
	if ( ( fd = open(argv[1], O_RDWR ) ) == -1)
	{write(2,"Cannot open for read/write \n",28); exit(1); }

	if ( fork ( )  )     /*  parent  */
	{
		for ( i =1; i <= 500; ++i  )
		{
			lseek ( fd, 0, SEEK_SET );
			read ( fd, &prom, sizeof ( int ) );
			prom += step1;
			sprintf(buf, "--------p1---> prom = %d\n", prom);
			write ( 1, buf, strlen ( buf ) ); 
			lseek ( fd, 0, SEEK_SET );
			write ( fd, &prom, sizeof ( int ) ); 
		}
	} else  {            /*   child   */

		for ( i =1; i <= 1000; ++i  )
		{
			lseek ( fd, 0, SEEK_SET );
			read ( fd, &prom, sizeof ( int ) );
			prom += step2;
			sprintf(buf, "-p2---> prom = %d\n", prom);
			write ( 1, buf, strlen ( buf ) ); 
			lseek ( fd, 0, SEEK_SET );
			write ( fd, &prom, sizeof ( int ) ); 
		}
	}
	write( 1, "Final value  ---->",18 );
	lseek ( fd, 0, SEEK_SET );
	read ( fd, &prom, sizeof ( int ) );
	sprintf(buf, " %d\n", prom); 
	write ( 1, buf, strlen ( buf ) ); 

}