/in/foo.cc: In function 'int main()':
/in/foo.cc:12:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |     while (i<a.size())
      |            ~^~~~~~~~~