/in/foo.cc: In function 'void erlar()':
/in/foo.cc:13:25: warning: iteration 1143263 invokes undefined behavior [-Waggressive-loop-optimizations]
         if (isnotprime[i]==false)
             ~~~~~~~~~~~~^
/in/foo.cc:12:18: note: within this loop
     for(int i=2;i<=maxn;i++){
                 ~^~~~~~