Simple geometry

#include <bits/stdc++.h>
const long double PI = acos(-1.0);

using namespace std;

struct Point
{
  int x, y;
  Point(int px = 0, int py = 0) : x(px), y(py) {}
};

struct Vector
{
  int x, y;
  Vector(int px = 0, int py = 0) : x(px), y(py) {};
  Vector(Point p1, Point p2) : x(p2.x - p1.x), y(p2.y - p1.y) {}
};

istream& operator>> (istream &in, Point & p)
{
  in >> p.x >> p.y;
  return in;
}

ostream& operator<< (ostream& out, const Vector & v)
{
  out << v.x << " " << v.y;
  return out;
}

int dot_product(Vector v1, Vector v2)
{
  return v1.x * v2.x + v1.y * v2.y;
}

int cross_product(Vector v1, Vector v2)
{
  return v1.x * v1.y - v1.y * v2.x;
}

signed main() {
  std::ios::sync_with_stdio(false);
  cin.tie(0);
  freopen("INPUT.TXT", "r", stdin);
  Point A, B, C;
  cin >> A >> B >> C;
  Vector AB(A,B), AC(A,C), BC(B,C);
  cout << AB << endl;
  cout << AC << endl;
  cout << BC << endl;
  return 0;
}