foo.cc: In function 'int main()':
foo.cc:9:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<=strlen(k)-1;++i)
                 ~^~~~~~~~~~~~~
foo.cc:13:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<=strlen(c)-1;++i)
                 ~^~~~~~~~~~~~~
foo.cc:29:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if(now>strlen(k)-1)
            ~~~^~~~~~~~~~~~

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