char * hoursToString(double h, char *str)
{
  int m = int(round(h * 60));
  int hr = (m / 60) % 24;
  int mn = m % 60;

  str[0] = (hr / 10) % 10 + '0';
  str[1] = (hr % 10) + '0';
  str[2] = ':';
  str[3] = (mn / 10) % 10 + '0';
  str[4] = (mn % 10) + '0';
  str[5] = '\0';
  return str;
}