Listing 2 time2.c — shows how to compute a date a given number of days in the future, as well as the elapsed execution time in seconds

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

main()
{
   time_t start, stop;
   struct tm *now;
   int ndays;

   /* Get current date and time */
   time(&start);
   now = localtime(&start);

   /* Enter an interval in days */
   fputs("How many days from now? ",stderr);
   if (scanf("%d",&ndays) !=1)
      return EXIT_FAILURE;
   now->tm_mday += ndays;
   if (mktime(now) != -1)
      printf("New date: %s",asctime(now));
   else
      puts("Sorry. Can't encode your date.");

   /* Calculate elapsed time */
   time(&stop);
   printf("Elapsed program time in seconds: %f\n",
     difftime(stop,start));

   return EXIT_SUCCESS;
}

/* Output
How many days from now? 45
New date: Fri Nov 20 12:40:32 1992
Elapsed program time in seconds: 1.000000
*/

/* End of File */