/in/foo.cc: In function 'int main()':
/in/foo.cc:14:9: warning: iteration 1000 invokes undefined behavior [-Waggressive-loop-optimizations]
   if(a[i]==1)
      ~~~^
/in/foo.cc:12:15: note: within this loop
  for(int i=1;i<=1001;i++)
              ~^~~~~~
/in/foo.cc:20:9: warning: iteration 1000 invokes undefined behavior [-Waggressive-loop-optimizations]
   if(a[i]==1)
      ~~~^
/in/foo.cc:18:15: note: within this loop
  for(int i=1;i<=1001;i++)
              ~^~~~~~
/in/foo.cc:15:7: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
    sum+=1;
    ~~~^~~