C经典算法之Eratosthenes筛选求质数

#include <stdio.h> 
#include <stdlib.h> 

#define N 1000 

int main(void) { 
    int i, j; 
    int prime[N+1]; 

    for(i = 2; i <= N; i++) 
        prime[i] = 1; 

    for(i = 2; i*i <= N; i++) { // 这边可以改进 
        if(prime[i] == 1) { 
            for(j = 2*i; j <= N; j++) { 
                if(j % i == 0) 
                    prime[j] = 0; 
            } 
        } 
    } 

    for(i = 2; i < N; i++) { 
        if(prime[i] == 1) { 
            printf("%4d ", i); 
            if(i % 16 == 0) 
                printf("\n"); 
        } 
    } 

    printf("\n");