/in/foo.cc: In destructor 'Persons::~Persons()':
/in/foo.cc:99:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < people.size(); i++) {
                         ~~^~~~~~~~~~~~~~~
/in/foo.cc: In member function 'void Persons::OutputPeople()':
/in/foo.cc:105:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < people.size(); i++) {
                         ~~^~~~~~~~~~~~~~~