iterative power 구현
int ft_iterative_power(int nb, int power) { int calc_nb; calc_nb = nb; if (nb >= 0 && power == 0) return (1); if (power < 0) return (0); if (nb > 0 && power > 0) { while (–power > 0) calc_nb *= nb; return (calc_nb); } return (0); }