foo.cc: In member function ‘void VectorArray::SelectSort()’:
foo.cc:79:31: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<Vector>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   79 |                 for (i = 0; i < a.size(); i++)
      |                             ~~^~~~~~~~~~
foo.cc:82:47: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<Vector>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   82 |                         for (int j = i + 1; j < a.size(); j++)
      |                                             ~~^~~~~~~~~~
foo.cc: In member function ‘void VectorArray::Output()’:
foo.cc:94:35: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<Vector>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   94 |                 for (int i = 0; i < a.size(); i++)
      |                                 ~~^~~~~~~~~~