User Timer in Linux/Unix

#include <sys/time.h >  
#include <signal.h >
#include <stdlib.h >
#include <stdio.h >

#define MAX_COUNT   100

/* This flag controls termination of the main loop. */
volatile sig_atomic_t counter = 0;

/* The signal handler just clears the flag and re-enables itself. */
void
catch_alarm (int sig)
{
    counter++;
    signal (sig, catch_alarm);
    //    printf("\nCatch an alarm!\n");
}


void do_stuff (void)
{
    static unsigned long c = 0;
    printf ("Doing stuff while waiting for alarm (myCounter = %u,    Counter=%u)          \r", ++c, counter);
}

void set_timer_val(struct itimerval *t, const unsigned long ival_usec, const unsigned int val_usec)
{
    //period between successive timer interrupts
    t->it_interval.tv_usec = ival_usec % 1000000;
    t->it_interval.tv_sec = ival_usec / 1000000;
    //period between now and the first timer interrupt
    t->it_value.tv_usec = val_usec % 1000000;
    t->it_value.tv_sec = val_usec / 1000000;
}

int main (void)
{
    struct itimerval ival, oval;

    /* Establish a handler for SIGALRM signals. */
    signal (SIGALRM, catch_alarm);

    /* Set an alarm to go off in a little while. */
    // one-shot timer
    set_timer_val(&ival, 1000000, 500000);
    setitimer (ITIMER_REAL, &ival, &oval);

    /* Check the flag once in a while to see when to quit. */
    while (counter < MAX_COUNT)
        do_stuff ();

    printf("\n");
    return EXIT_SUCCESS;
}