foo.cc: In function ‘int main()’:
foo.cc:13:34: 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 = 0; i < s.length(); i++)
      |                                ~~^~~~~~~~~~~~
foo.cc:41:34: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   41 |                 for(int j = 0; j < st[i].length(); j++)
      |                                ~~^~~~~~~~~~~~~~~~