profiling linux code nanosec

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

/*
struct timespec {
    time_t tv_sec;  //seconds
    long tv_nsec;   //nanoseconds
};

CLOCK_REALTIME
CLOCK_PROCESS_CPUTIME_ID
CLOCK_THREAD_CPUTIME_ID

startTime = clock_gettime(CLOCK_PROCESS_CPUTIME_ID,&t1);
endTime = clock_gettime(CLOCK_PROCESS_CPUTIME_ID,&t2);
elapsed CPU time: endTime - startTime;

*/

// profiling code using clock_gettime article https://www.guyrutenberg.com/2007/09/22/profiling-code-using-clock_gettime/

struct timespec diff(struct timespec start,struct timespec end)
{
    struct timespec temp;

    if ((end.tv_nsec-start.tv_nsec)<0) {
        temp.tv_sec = end.tv_sec-start.tv_sec-1;
        temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
    } else {
        temp.tv_sec = end.tv_sec-start.tv_sec;
        temp.tv_nsec = end.tv_nsec-start.tv_nsec;
    }

    return temp;
}


int
main (int argc, char **argv)
{

    struct timespec time1, time2;

    int a = 0;

    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);

    for(int i = 0;i<100;i++)
    {
        a++;
    }

    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time2);

    printf("a: %d\n", a);

    //printf("%ld:%ld\n",diff(time1,time2).tv_sec, diff(time1,time2).tv_nsec);
    printf("%ld:%09ld\n",diff(time1,time2).tv_sec, diff(time1,time2).tv_nsec);

    clock_gettime(CLOCK_REALTIME, &time1);

    sleep(1);

    clock_gettime(CLOCK_REALTIME, &time2);

    //printf("%ld:%ld\n",diff(time1,time2).tv_sec, diff(time1,time2).tv_nsec);
    printf("%ld:%09ld\n",diff(time1,time2).tv_sec, diff(time1,time2).tv_nsec);

    return 0;
}