C++ inherit from a concrete class to another concrete class - c++

Question

I'm trying to inherit from one of my class 2 variables which they must be equal to be able to return the value of one of my functions in the other class..
class Rectangle: public Shape{
double Length;
double Width;
public:
Rectangle(double Length, double Width):
Shape("Rectangle")
{
this->Length=Length;
this->Width=Width;
}
double getPerimerter(){
return 2 * (Length+Width);
}
double getArea(){
return Length * Width;
}
};
class Square: public Shape, public Rectangle{
double Side;
public:
Square():
Shape("Square"),
Rectangle(Length,Width)
{}
double getPerimerter(){
if(Length==Width)
return 4 * (Length+Width);
}
double getArea(){
if(Length==Width)
return (Length+Width) * (Length+Width);
}
};
as you can see I have already a concrete class call Rectangle which hold to private variables with the names Length and Width.. What I'm trying to do is inherit this class to my class Square and if Length and Width are equal then I can return the Area and Perimeter of the Square..

Answer 1

It is perfectly fine to inherit from an existing class.
What you probably want, however, is this:
class Square: public Rectangle
{
public:
Square(double Side) : Rectangle(Side, Side) { }
};
That way, there is no problem of someone trying to use a ractangular square Square(4.3, 9.6).
Alternatively, you could of course use typedef Rectangle Square;
Edit:
To overcome the "name", we could do something like this:
class Rectangle
{
public:
Rectangle(double Length, double Width) : Shape("Rectangle") { ... }
protected:
Rectangle(double Length, double Width, const char *name) : Shape(name), Length(Length), Width(Width) {}
};
class Square
{
public:
Square(double side) : Rectangle(side, side, "Square") {}
};
Edit2: Code that I came up with:
#include <iostream>
using namespace std;
class Shape
{
private:
const char *name;
public:
Shape(const char *name) : name(name) {}
virtual double getPerimeter() = 0;
virtual double getArea() = 0;
};
class Rectangle: public Shape{
double Length;
double Width;
public:
Rectangle(double Length, double Width):
Shape("Rectangle")
{
this->Length=Length;
this->Width=Width;
}
double getPerimeter(){
return 2 * (Length+Width);
}
double getArea(){
return Length * Width;
}
protected:
Rectangle(double Length, double Width, const char *name):
Shape(name)
{
this->Length=Length;
this->Width=Width;
}
};
class Square: public Rectangle
{
public:
Square(double Side):
Rectangle(Side,Side, "Square")
{
}
};
int main()
{
Square sq(10.0);
Rectangle rect(12.0, 4.0);
cout << "sq:" << sq.getArea() << " rect:" << rect.getArea() << endl;
}

Answer 2

As a first thing you should add an argument to Square constructor, like so:
Square(double Side):Rectangle(Side,Side){
// Add additional constructor code here if required
}
About returning a value in a constructor - that is a no-go as the constructor might not return anything.
I hope this is what you meant as your question was quite hard for me to understand.

Answer 3

I might not understand your question, but it looks to me like you only need to add a parameter to your Square() constructor. It would look like this:
class Square: public Rectangle{
public:
Square(double dimension):
Rectangle(dimension, dimension){
}
};
There is no need for a conditional statement in the Square() constructor. Creating a Square necessarily implies creating a Rectangle with equal length and width.