/in/foo.cc: In function 'int main()':
/in/foo.cc:30:12: warning: unused variable 'j' [-Wunused-variable]
  int n, i, j, top;
            ^
/in/foo.cc:30:15: warning: unused variable 'top' [-Wunused-variable]
  int n, i, j, top;
               ^~~