/in/foo.cc: In function 'void build_max_heap(int*, int)':
/in/foo.cc:49:6: warning: unused variable 'heap_size' [-Wunused-variable]
  int heap_size=len;
      ^~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:68:6: warning: unused variable 'j' [-Wunused-variable]
  int j=clock();
      ^
/in/foo.cc:83:6: warning: unused variable 'l' [-Wunused-variable]
  int l=clock();
      ^