/in/foo.cc: In function 'bool huiwen()':
/in/foo.cc:40:8: warning: statement is a reference, not call, to function 'exit' [-Waddress]
    exit;
        ^
/in/foo.cc:40:8: warning: statement has no effect [-Wunused-value]
/in/foo.cc: In function 'int main()':
/in/foo.cc:50:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<s.size();i++)
          ~^~~~~~~~~