Weird behaviour of overloaded + operator - c++

Question

I have made class which represents Line Linia (aX+bY=c) and I overloaded + operator so now it now returns new Linia object which has c = c + b/argument. But the problem is that when I use this operator all the fields of the given Line object become 0
#include <iostream>
using namespace std;
struct Q{
public:
double x,y;
Q(double x, double y){
this->x = x;
this->y = y;
}
friend ostream& operator<< (ostream &wyjscie, Q const& ex){
wyjscie<<"("<<ex.x<<","<<ex.y<<")";
return wyjscie;
}
};
class Linia{
public:
double a,b,c;
Linia (double a, double b, double c){
this->a = a;
this->b = b;
this->c = c;
}
Linia operator+ (double i){
return Linia(a, b, c + i/b);
}
Linia operator- (double i){
return Linia(a, b, c - i/b);
}
Q operator* (const Linia& i){
double w = a*i.b - b*i.a;
double wx = -c*i.b + i.c*b;
double wy = a*(-i.c) + i.c*c;
double x = wx/w, y = wy/w;
cout<<*this<<endl;
cout<<i<<endl;
return Q(x,y);
}
friend ostream& operator<< (ostream &wyjscie, Linia const& ex){
wyjscie<<ex.a<<"x + "<<ex.b<<"y = "<<ex.c;
return wyjscie;
}
};//podwyzszenie przez ile/B
int main()
{
Linia* pionowa = new Linia(0,1,0);
Linia* l = new Linia(1,1,3);
// Q q = (*l) * (*pionowa);
cout<<"linia przed podniesieniem "<<*l<<endl;
// cout<<"punkt przeciecia przed podniesieniem: "<<q<<endl;
l = l+3;
cout<<"Line highered"<<*l<<endl;
l = l-3;
cout<<"Line Lowered "<<*l<<endl;
// q = (*l) * (*pionowa);
// cout<<"punkt przeciecia po podniesieniu: "<<q<<endl;
cout << "Hello world!" << endl;
return 0;
}

Answer 1

You are doing pointer arithmetic here. That means that l ends up pointing to some address where is shouldn't:
Linia* l = new Linia(1,1,3);
l = l+3; // l is a pointer!!!
If you stop using new and raw pointers everywhere it might just work.
int main()
{
Linia pionowa(0,1,0);
Linia l(1,1,3);
l = l+3;
cout<<"Line highered"<< l <<endl;
l = l-3;
cout<<"Line Lowered "<< l <<endl;
}