/in/l8.cpp: In member function 'int Calculator::calculate()':
/in/l8.cpp:208:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
  for(int i = 0; i < s.size(); i ++){   //�����ַ��� 
                 ~~^~~~~~~~~~
/in/l8.cpp: In function 'int main(int, char**)':
/in/l8.cpp:259:8: error: variable 'result' set but not used [-Werror=unused-but-set-variable]
    int result = 0;
        ^~~~~~
/in/l8.cpp: In member function 'int Calculator::calculate()':
/in/l8.cpp:248:1: error: control reaches end of non-void function [-Werror=return-type]
 }
 ^
cc1plus: all warnings being treated as errors