/in/foo.cc: In function 'int main()':
/in/foo.cc:11:15: warning: iteration 99998 invokes undefined behavior [-Waggressive-loop-optimizations]
         if(p[i]==0) prime[++cnt]=i;
            ~~~^
/in/foo.cc:10:18: note: within this loop
     for(int i=2;i<=maxn;++i){
                 ~^~~~~~