#include <stdio.h>      /* puts, printf */

#include <time.h>       /* time_t, struct tm, time, localtime */

int main ()

{

    struct tm * timeinfo;

    double seconds;

    time_t start_time,now;

    time (&start_time);

    while(){

        time (&now);

        seconds = difftime(now,start_time);

        if(seconds==){

            break;

        }

    }

    timeinfo = localtime (&start_time);

    printf ("start_time local time and date: %s", asctime(timeinfo));

    timeinfo = localtime (&now);

    printf ("now local time and date: %s", asctime(timeinfo));

    printf("time spend %f\n",seconds);

    return ;

}

start_time local time and date: Fri May  ::

now local time and date: Fri May  ::

time spend 5.000000