foo.cc: In function 'int main()':
foo.cc:9:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |  for(int i=0;i<s.size();i++)
      |              ~^~~~~~~~~
foo.cc:18:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |  for(int i=1;i<sf.size();i++)
      |              ~^~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务