foo.cc: In function ‘int main()’:
foo.cc:16:23: warning: iteration 1004 invokes undefined behavior [-Waggressive-loop-optimizations]
   16 |                 if(a[i]!=0)
      |                    ~~~^
foo.cc:15:22: note: within this loop
   15 |         for(int i=1;i<=1005;i++)
      |                     ~^~~~~~