a121. 質數又來囉

#include 

using namespace std;

#include 



int main()

{

    int a,b;

    while(cin>>a>>b)

    {

                   int prime_num=0; 

                   for(int num=a;num<=b;num++)

                   {

                           if (num==1) continue;

                           else if(num==2){ prime_num++;continue;}

                           else if(num==3) { prime_num++;continue;}

                           else 

                           {

                                int flag_isprime=1;

                                for(int factor=2;factor<=sqrt(num)+1;factor++)

                                        if(num%factor==0){flag_isprime=0;break;}

                                if (flag_isprime==1)

                                   prime_num++;

                           }

                   }

                   cout<    }

    return 0;

}