Function is_happy

ch1-c-threads/happycoin.c:26–31

}

bool is_happy(uint64_t num) {
  while (num != 1 && num != 4) {
    num = sum_digits_squared(num);
  }
  return num == 1;
}

bool is_happycoin(uint64_t num) {
  return is_happy(num) && num % 10000 == 0;