foo.cc: In function 'int hf(std::string)':
foo.cc:8:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 | for(register int i=0;i<st.size();++i){
      |                      ~^~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务