overloaded * operator work only with one construktor

Question

I have class:

class Cline
{
public:

    Cline ():ax(1),by(1),c(0){}
    Cline (double aa, double bb,double cc):ax(aa*(-1)),by(bb),c(cc){

        if(by==0){ 
            exit(1);    
        }   
    }


    Pkt operator* (const Cline & p) 
        {
            if(p.ax != this->ax)    
                {
                      Pkt pkt;
                      double x=this->ax+(p.ax*(-1));
                      double c=(this->c*-1)+p.c;

                      pkt.x=c/x;
                      pkt.y=(this->ax*pkt.x+this->c)/this->by;  

                      return pkt;   
                }
            else 
                {
                    cout<<"no connection";
                }
        }

     void setAX(double w){ax=w;}    
     void setBY(double w){by=w;}
     void setC(double w){c=w;}

     double getAX(){return ax;} 
     double getBY(){return by;}
     double getC(){return c;}

private:

    double ax;
    double by;
    double c;
};

when I use two times second constructor:

int main()
{   

Cline z(1,1,1);
Cline w(4,3,-12);

z*w;

return 0;
}

everything is ok but when I use first and second constructor:

 int main()
 {  

Cline z();
Cline w(4,3,-12);

z*w;

return 0;
}

I recive error:

 "no match for operators 'z*w' "

Could somebody tell me what I am doing wrong? I have no idea when lies my mistake :(

Answer 1

The problem is that, in C++, this is a function declaration of a function called z, that has no parameters, and returns a Cline by value:

Cline z();

You need

Cline z;   // C++03 and C++11

or

Cline z{}; // C++11