foo.cc: In constructor 'Date::Date(std::string)':
foo.cc:33:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |         while (index < s.length()) {
      |                ~~~~~~^~~~~~~~~~~~
foo.cc: In member function 'void Persons::print()':
foo.cc:133:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Person*>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  133 |         for (int i = 0; i < v.size(); i++) {
      |                         ~~^~~~~~~~~~

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