foo.cc: In function 'int jud(std::__cxx11::string, std::__cxx11::string, std::__cxx11::string)':
foo.cc:9:20: warning: left operand of comma operator has no effect [-Wunused-value]
     for(i=0,j=n-1;i<=n-1,j>=0;i++,j--)
                   ~^~~~~