In file included from main.cpp:16:0:
set.h: In constructor 'Set::Set(const std::vector<long int>&)':
set.h:18:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < vec.size(); i++) {
                 ~~^~~~~~~~~~~~
set.h: In member function 'Set Set::Union(const Set&)':
set.h:29:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < s.S.size(); i++) {
                 ~~^~~~~~~~~~~~
set.h:35:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < this->S.size(); i++) {
                 ~~^~~~~~~~~~~~~~~~
set.h: In member function 'Set Set::Intersection(const Set&)':
set.h:46:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < s.S.size(); i++) {
                 ~~^~~~~~~~~~~~
set.h: In member function 'Set Set::Difference(const Set&)':
set.h:55:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < s.S.size(); i++) {
                 ~~^~~~~~~~~~~~
set.h: In member function 'Set Set::SymmetricDifference(const Set&)':
set.h:64:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < s.S.size(); i++) {
                 ~~^~~~~~~~~~~~
set.h:69:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < this->S.size(); i++) {
                 ~~^~~~~~~~~~~~~~~~
set.h: In member function 'bool Set::Contains(int64_t)':
set.h:82:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < this->S.size(); i++) {
                 ~~^~~~~~~~~~~~~~~~
set.h: In member function 'void Set::Remove(int64_t)':
set.h:90:19: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
 for (int i = 0; i < this->S.size(); i++) {
                 ~~^~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors