foo.cc: In function 'int main()':
foo.cc:29:50: warning: 'op' may be used uninitialized in this function [-Wmaybe-uninitialized]
         for (i = n - 1; i >= 0; i--) cout << op[i];
                                              ~~~~^

自豪地采用[jd5](https://github.com/masnn/jd5)进行评测