8，求2~n的素数和

 1 int test8(int num){
 2     int i,j,k;
 3     long sum = 2;
 4     int sqr ;
 5     if(num<=2)
 6         return 0;
 7     for(i=3; i<num; i+=1){
 8         k=1;
 9         sqr = (int)sqrt(i);
10         for(j=2; j<=sqr; j++){
11             if(i%j==0){
12                 k = 0;
13                 break;
14             } 
15         }
16         if(k)
17             sum += i;
18     }
19     return sum;
20 }