/in/foo.cc: In function 'bool cmp(std::__cxx11::string, std::__cxx11::string)':
/in/foo.cc:9:9: warning: unused variable 'len' [-Wunused-variable]
     int len=a.length(),i;
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:15:8: warning: unused variable 'x' [-Wunused-variable]
  int n,x;
        ^