In file included from main.cpp:16:0:
set.h: In member function 'Set Set::Union(const Set&) const':
set.h:9:24: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
      for (int i = 0; i < b.myset.size(); i++) {
                      ~~^~~~~~~~~~~~~~~~
set.h: In member function 'Set Set::Intersection(const Set&) const':
set.h:17:24: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
      for (int i = 0; i < myset.size(); i++) {
                      ~~^~~~~~~~~~~~~~
set.h:18:26: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
        for (int j = 0; j < b.myset.size(); j++) {
                        ~~^~~~~~~~~~~~~~~~
set.h: In member function 'Set Set::Difference(const Set&) const':
set.h:28:24: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
      for (int i = 0; i < b.myset.size(); i++) {
                      ~~^~~~~~~~~~~~~~~~
set.h: In member function 'Set Set::SymmetricDifference(const Set&) const':
set.h:38:24: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
      for (int i = 0; i < c_.size(); i++) {
                      ~~^~~~~~~~~~~
cc1plus: all warnings being treated as errors