Polymorphism (shapes) object

[luis123]

Hi everyone! Im doing a classic example of polymorphism with shapes but im stuck with the first example of a shape (circle) which is a derived class from the base (shapes). The problem is that i can´t create an object of the class circle and i dont understand why.... can someone help me?

 #include <iostream>
#include <string>
#include <list>
#include <cmath>

using namespace std;

class Shape{
   
public:
    virtual void setX(int xcor);
    virtual void setY(int ycor);
    virtual int getX(); 
    virtual int getY();
    virtual double area();
    virtual double perimetro();
};

class Circle : public Shape {
private:
    int x, y;
    double raio;
public:
	Circle(int xcor , int ycor , double r){
        x = xcor;
        y = ycor;
        raio = r;
    }
    
    void setX(int xcor){
         x = xcor;
    }
    void setY(int ycor){
        y = ycor;
    }
    
    void set_raio(double r){
        raio = r;
    }
    
    double get_raio(){
        return raio;
    }
    
    int getX(){
        return x;
    }
    
    int getY(){
        return y;
    }
    
    double area(){
        return ((pow(2,raio))* 3.14);
    }
	double perimetro(){
        return ((raio * 2) * 3.14);
    }
};

int main()
{
    Circle ob(2,3,2); // when I create and object i get error 


}

[coder777]

you need to implement all functions you declared unless you make them pure virtual like

virtual void setX(int xcor) = 0;

then you need to implement the function in the derived class

[NVTKrishna]

Hi luis123,

You have declared funtions in the base class but definition are not present, that is why your getting errors.

Please provide the function definition or mark the funtion as pure virtual (=0).

Modified Code is shown in bold

class Shape{
   
public:
    virtual void setX(int xcor)=0;
    virtual void setY(int ycor)=0;
    virtual int getX()=0; // const ?
    virtual int getY()=0;
    virtual double area()=0;
    virtual double perimetro()=0;
};

[Aceix]

For the initialization of an instance of Shape(or Circle) to be possible, there must be an implementation of Shape::setX(int), Shape::setY(int) and all Shape functions which aren't pure virtual(in this case, all).
So since you do not need implementation of the general class(as implied in your code), you could do this:

virtual void setX(int xcor){}
virtual void setY(int ycor){}
virtual int getX() const {}
virtual int getY() const {}
virtual double area(){}
virtual double perimetro(){}

Aceix;

[luis123]

Thank you everyone! I understood the concept and I can now code with no errors :D . Greeting to erveryone!