素数筛选法

原理见百度百科：<span style="font-size:18px; font-family: 'Microsoft YaHei', SimHei, Verdana; line-height: 34px;"><a target=_blank href="http://baike.baidu.com/link?url=tnflbaX0lq34F51rXEWAL8cNkLZ6N9H9o-j0g6qA-L5QT4Zz5zVs1jrT_7zLqCUCGJ5Cpi7oxiookVTKI0HKC_" target="_blank">筛法求素数</a></span>

#define range 20
bool IsPrime[range + 1];
void set(bool IsPrime[])
{
int i, j;
for (i = 0; i <= range; ++i)
IsPrime[i] = true;
IsPrime[0] = IsPrime[1] = false;
for (i = 2; i <= range; ++i)
{
if (IsPrime[i])
{
for (j = 2 * i; j <= range; j += i)
IsPrime[j] = false;
}
}
}