用筛法求之N内的素数。(N < 1000000)

来源:http://my.oschina.net/dianpaopao/blog/83844

#include<stdio.h>
#include<stdlib.h>
#define NMAX 10000000
#define SQRN 10000
int main()
{
    int n;
    scanf("%d",&n);
    static char a[NMAX];
    unsigned long k,i;
    for(k=2;k<=SQRN;k++)
        if(!a[k])
			for(i=2*k;i<n;i+=k)
               a[i]=1;
    for(i=2;i<n;i++)
        if(!a[i])  printf("%ld\n",i);
    return 0;
}

PS:出处下面的评论更强大,还在理解中ing...