foo.cc: In function 'int main()':
foo.cc:11:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size();i++){//移项变号
               ~^~~~~~~~~
foo.cc:18:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<s.size();i++){
               ~^~~~~~~~~
foo.cc:36:38: error: cannot convert 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'int' for argument '1' to 'std::_Setprecision std::setprecision(int)'
   cout<<c<<'='<<fixed<<setprecision(s)<<csx/ycx;
                                      ^

[Hydro](https://hydro.ac)提供评测服务