foo.cc: In function 'int main()':
foo.cc:9:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < s.size(); i++) {
                     ~~^~~~~~~~~~
foo.cc:27:19: warning: value computed is not used [-Wunused-value]
             c[m++]==s[i];
foo.cc:11:29: warning: 'c[<unknown>]' may be used uninitialized in this function [-Wmaybe-uninitialized]
             if (m>0&&c[m - 1] == '(')
                      ~~~~~~~^
foo.cc:19:29: warning: 'c[<unknown>]' may be used uninitialized in this function [-Wmaybe-uninitialized]
             if (m>0&&c[m - 1] == '[')
                      ~~~~~~~^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。