/in/foo.cc: In function 'int main()':
/in/foo.cc:16:7: warning: iteration 19999 invokes undefined behavior [-Waggressive-loop-optimizations]
   16 |   a[i]=num;
      |   ~~~~^~~~
/in/foo.cc:14:16: note: within this loop
   14 |   for(int i=1;i<=20000;i++){
      |               ~^~~~~~~