const int MAX_NUM = 100001;
unsigned char isPrime[MAX_NUM];

void GetPrime (void)
{
    memset(isPrime, 1, sizeof(isPrime));

    isPrime[0] = isPrime[1] = 0;

    for (int i = 2; i*i < MAX_NUM; i++)
        if (isPrime[i])
            for (int j = i*i; j < MAX_NUM; j += i)
                isPrime[j] = 0;
}