foo.cc: In function ‘std::vector<int> Diff(std::vector<int>&, std::vector<int>&)’:
foo.cc:8:27: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    8 |         for (int i = 0; i < va.size(); i++)
      |                         ~~^~~~~~~~~~~
foo.cc:11:35: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   11 |                 for (int j = 0; j < vb.size(); j++)
      |                                 ~~^~~~~~~~~~~
foo.cc: In function ‘void Output(std::vector<int>&)’:
foo.cc:23:27: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   23 |         for (int i = 0; i < vc.size(); i++)
      |                         ~~^~~~~~~~~~~