C++ 관련 질문입니다

#include<iostream>
struct Vector2
{
	int x, y;
};
struct Vector4
{
public:
	union
	{
		struct
		{
			int x, y, z, w;
		};
		struct
		{
			Vector2 a, b; //부분 (가)
		};
	};
};
void PrintVector(const Vector2& vector)
{
	std::cout << vector.x << ", " << vector.y << std::endl;
}
int main()
{
	Vector4 vector4 = { 1,2,3,4 };
	PrintVector(vector4.a);
	PrintVector(vector4.b);
	vector4.x = 50;
	PrintVector(vector4.a);
	PrintVector(vector4.b);
	std::cin.get();
}