Simple Countdown Timer

timer.c

/* Copyright 2017 Taeber Rapczak
 *
 * Simple countdown timer
 *
 * EXAMPLES
 *  $ timer 10     # sets timer for 10 seconds
 *  $ timer 1m     # sets timer for 1 minute
 *  $ timer 3h5m2  # sets timer for 3 hours, 5 minutes, 2 seconds
 */

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

unsigned parse(char text[])
{
  unsigned
    hours = 0,
    minutes = 0,
    seconds = 0;

  char current;

  for (unsigned i = 0; (current = text[i]) != '\0'; i++) {
    if (current == 'h') {
      hours = seconds;
      minutes = seconds = 0;
    } else if (current == 'm') {
      minutes = seconds;
      seconds = 0;
    } else if (isdigit(current)) {
      seconds = (seconds*10) + (current-'0');  /* ASCII math */
    }
  }

  return hours*3600 + minutes*60 + seconds;
}

int main(int argc, char *argv[])
{
  unsigned remaining;  /* seconds remaining */
  remaining = argc == 2? parse(argv[1]): 0;
  printf("Timer: %d seconds\n", remaining);

  for (; remaining > 0; remaining--) {
    printf("\r%02d:%02d:%02d",
        remaining/3600,      /* hours */
        (remaining%3600)/60, /* minutes */
        remaining%60         /* seconds */
    );
    fflush(stdout);
    sleep(1);
  }

  printf("\r00:00:00\a\n");  /* ring the bell! */

  return 0;
}