筛选法产生素数表

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
//prime[i]
//if prime[i] = 1  then i is prime number;
//otherwise i isn't prime number!
char* solve(int n)
{
    int i, j;
    char *prime = NULL;
    
    prime = (char*)malloc(sizeof(char) * ( n + 1));
    for(i = 0; i < n; ++i)
        prime[i] = 1;
    prime[0] = 0;
    prime[1] = 0;
    for(i = 2; i <= sqrt(n); ++i)
    {
        if(prime[i])
        {
            for(j = 2 * i; j <= n; j += i)
                prime[j] = 0;
        }
    }
    return prime;
}
void print(char *a, int n)
{
    int i;
    for(i = 0; i <= n; ++i)
    {
        if(a[i])
        {
            printf("%d\t", i);
        }
    }
    printf("\n");
}
int main()
{
    int n;
    while(scanf("%d", &n) && n >=2)
    {
        time_t t1 = clock();
        char *prime = solve(n);
        time_t t2 = clock();
        
        print(prime, n);
        printf("time:%f\n", (t2 - t1) * 1.0 / CLOCKS_PER_SEC);
        free(prime);
    }
    return 0;
}

/////////////以下是产生素数表的关键代码

for(i = 0; i < n; ++i) 
prime[i] = 1; prime[0] = 0;
prime[1] = 0; for(i = 2; i <= sqrt(n); ++i)
{
 	if(prime[i]) 
	{ 
		for(j = 2 * i; j <= n; j += i)
 			prime[j] = 0;
 	} 
}