/in/foo.cc: In function 'int main()':
/in/foo.cc:17:14: warning: iteration 100000 invokes undefined behavior [-Waggressive-loop-optimizations]
   a[i]+=a[i-1];
              ^
/in/foo.cc:15:15: note: within this loop
  for(int i=1;i<=100001;i++)
              ~^~~~~~~~