Question

I am trying to solve a lesson in my study. I am going to have an abstract class, CFigure, on top and different figures below, currently I have made a circle class. I am going to call this from a C# program.

But when I try to build my code I get the following error messages:

• unresolved token (06000001) arealBeregnerCPP.CFigure::area
• unresolved token (06000002) arealBeregnerCPP.CFigure::circumference
• 2 unresolved externals

I hope anyone can give me a hint in what I do wrong… Thanks!

This is my program:

// arealBeregnerCPP.h

#pragma once

using namespace System;

namespace arealBeregnerCPP {

    public ref class CFigure
    {
    public:
        virtual double area();
        virtual double circumference();
    };

    public ref class CCircle : public CFigure
    {
    private:
        double m_radius;

    public:
        CCircle(double radius) 
        {
            m_radius = radius;
        }

        virtual double area() override
        {
            return 0; //not implementet
        }

        virtual double circumference() override
        {
            return 0; //not implementet
        }       
    };
}

Answer 1

if CFigure::area() and CFigure::circumference() are abstract functions then put = 0 in declaration:

    virtual double area() = 0;
    virtual double circumference() = 0;