foo.cc: In function 'int main()':
foo.cc:13:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |     for(int i=1;i<=a.size()-1;i++)
      |                 ~^~~~~~~~~~~~
foo.cc:20:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |     for(int i=0;i<=a.size()-2;i++)
      |                 ~^~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务