参考方案：

#include <stdio.h>
#include <math.h>
#include <stdbool.h>
#include <stdlib.h>
#include <sys/time.h>

//素数判定 筛选法
int main(){
    int num = 100;
    int i, j;
    //scanf("%d", &num);
    //getchar();
    bool *b;
    b=(bool *)calloc(num + 1, sizeof(bool));
    b[0] = false;
    for(i = 1; i <= num; i++){
        if(i % 2 == 0){
           b[i] = false;
        }else{
           b[i] = true;
        }
    }

    for(int i = 3; i <= sqrt(num); i+=2){
        if(b[i]){
            for(j=i+i; j <= num; j+=i)
                b[j] = false;
        }
    }

    
    //输出素数
    printf("2,");    
    for(i = 3; i <= num; i+=2){
       if(b[i]){
           printf("%d,", i);
       }
    }

    free(b);
    b=NULL;
    return 0;
}