foo.cc: In function 'int main()':
foo.cc:36:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<exp.size();i++)
                 ~^~~~~~~~~~~
foo.cc: In function 'int priority(char)':
foo.cc:29:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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