/in/foo.cc: In function 'int main()':
/in/foo.cc:13:10: warning: unused variable 'arr' [-Wunused-variable]
     int *arr=(int *)malloc(sizeof(int)*1000000);
          ^~~
/in/foo.cc:17:16: error: 'sort' was not declared in this scope
  sort(arr,arr+n);
                ^