foo.cc: In function 'int main()':
foo.cc:7:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |     for (int i = 0; i < s.size(); i++)
      |                     ~~^~~~~~~~~~
foo.cc:15:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |         if(i==s.size()-1)
      |            ~^~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务