/in/foo.cc: In function 'int main()':
/in/foo.cc:9:7: warning: iteration 47 invokes undefined behavior [-Waggressive-loop-optimizations]
   a[i]=a[i-2]+a[i-1];
   ~~~~^~~~~~~~~~~~~~
/in/foo.cc:8:15: note: within this loop
  for(int i=3;i<=50;i++){
              ~^~~~