foo.cc: In function 'int main()':
foo.cc:11:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |         for(int i = 0; i < str.size(); i++) ch[i+1] = str[i];
      |                        ~~^~~~~~~~~~~~
foo.cc:16:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |                 for(int i = 1; i <= str.size(); i++)
      |                                ~~^~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务