/in/foo.cc:4:0: warning: ignoring #pragma optimize  [-Wunknown-pragmas]
 #pragma optimize (2)
 
/in/foo.cc: In function 'void add(int, int)':
/in/foo.cc:24:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i = p; i <= n; i += lowbit(i)) bit[i] += x; return;
  ^~~
/in/foo.cc:24:54: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  for(int i = p; i <= n; i += lowbit(i)) bit[i] += x; return;
                                                      ^~~~~~