Класс Line, вычисление угла в радианах

Line::Line() {};
Line::Line(double a, double b, double c) {
    this->a = a;
    this->b = b;
    this->c = c;
}
void Line::SetA(double a) { this->a = a; }
void Line::SetB(double b) { this->a = b; }
void Line::SetC(double c) { this->a = c; }
double Line::GetA() { return a; }
double Line::GetB() { return b; }
double Line:: GetC() { return c; }
double Line::GetRad() { return Rad; }
double Line::GetDeg() { return deg; }
double Line::IntersectionX(double a, double b, double c) {
    double IntSec;
    this->a = a;
    this->b = b;
    this->c = c;
    IntSec = (-c) / a;
    return IntSec;
}
double Line::IntersectionY(double a, double b, double c) {
    double IntSec;
    this->a = a;
    this->b = b;
    this->c = c;
    IntSec = (-c) / b;
    return IntSec;
}
double Line::RadToDeg(double Rad)
{
    return Rad * (180.0 / (atan(1) * 4));
}
 
 
void Line::operator ++(){
    this->deg += 1;
}

class Line {
    double a;
    double b;
    double c;
    double Rad = atan(a / b);
    double deg = Rad * (180.0 / (atan(1) * 4));;
public:
    Line();
    Line(double a, double b, double c);
    void SetA(double a);
    void SetB(double b);    
    void SetC(double c);
    double GetA();
    double GetB();
    double GetC();
    double GetRad();
    double GetDeg();
    double IntersectionY(double a, double b, double c);
    double IntersectionX(double a, double b, double c);
    double RadToDeg(double Rad);
    void operator ++();
};

double GetRad(){ return  atan2(a , b); }
 double GetDeg(){ return Rad() * 180.0 / M_PI; }

Line& operator++()// префиксный инкремент
{
    double alfa=(GetDeg()+1.)*M_PI/180.;
    a=tan(alfa)*b;
    return *this;
}
Line operator++(int)// постфиксный инкремент
{
    Line tmp(*this);
    double alfa=(GetDeg()+1.)*M_PI/180.;
    a=tan(alfa)*b;
    return tmp;
}