/in/foo.cc: In function 'bool KFC(std::__cxx11::string, std::__cxx11::string)':
/in/foo.cc:7:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i <= y.size() - x.size(); i++) {
                  ~~^~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:10:4: error: 'sss' was not declared in this scope
    sss += y[k];
    ^~~
/in/foo.cc:12:11: error: 'sss' was not declared in this scope
   cout << sss << "\n";
           ^~~