/in/foo.cc: In function 'int main()':
/in/foo.cc:8:35: warning: iteration 998 invokes undefined behavior [-Waggressive-loop-optimizations]
  for(int i = 2;i<1001;i++) num[i] = num[i-2]+num[i-1];
                            ~~~~~~~^~~~~~~~~~~~~~~~~~~
/in/foo.cc:8:17: note: within this loop
  for(int i = 2;i<1001;i++) num[i] = num[i-2]+num[i-1];
                ~^~~~~