Вектор на плоскости: координаты вектора на плоскости (x1, y1, x2, y2). Вычислить координаты середины вектора. Равен ли у

#include <iostream>
#include <cmath>
 
#define PI 3.14159265
 
class vec
{
public:
    float x1;
    float y1;
    float x2;
    float y2;
 
    vec() {}
    vec(float _x1, float _y1, float _x2, float _y2) { x1= _x1; y1= _y1; x2 = _x2; y2 = _y2;}
    ~vec() { std::cout << "destructed\n"; }
 
    void mid() { float sx = (x1 + x2) / 2; float sy = (y1 + y2) / 2;  std::cout << "mid: (" << sx << " " << sx << ") \n";}
    float len() { float d = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)* (y1 - y2));  return d; }
    float cosx() { float a = ((x2 - x1) / len());  std::cout << "cx " << a << "\n";  return a; }
    float cosy() { float a = ((y2 - y1) / len()); std::cout << "cy " << a << "\n";  return a; }
    void print() { std::cout << "(" << x1 << " " << y1 << ") " << "(" << x2 << " " << y2 << ")\n "; }
};
 
#define EPSILON 0.01
 
bool CompareDoubles2(double A, double B)
{
    float diff = A - B;
    return (diff < EPSILON) && (-diff < EPSILON);
}
 
int main()
{
    vec a(1,1,2,2);
    a.print();
    a.mid();
    std::cout << "d " << a.len() << "\n"; 
    if ( CompareDoubles2(a.cosx(), (cos(45 * PI / 180)))    )   { std::cout << "45\n"; };
    if (CompareDoubles2(a.cosy(), (cos(45 * PI / 180)))) { std::cout << "45\n"; };
 
    return 0;
}