Displaying results of methods on the screen - c++

Question

My task is to practice inheritance, putting all the classes in separate files. I have a base class Circle and a derived class Cylinder.
What I'm stuck on is trying to display on the screen the result of my calculated area and volume for an object B of a Cylinder type. I found a way to do that for a Circle, though it doesn't work for my Cylinder.
circle.h
#pragma once
#include <iostream>
class Circle {
public:
float r;
Circle();
Circle(float r);
Circle circumference();
Circle area();
void view();
void getArea();
void getCircum();
};
circle.cpp
#include "circle.h"
#include <cmath>
using namespace std;
Circle::Circle() : r(5) {
cout << "Default constructor has been called for a circle\n";
}
Circle::Circle(float r) {
this->r = r;
cout << "Constructor with parameters has been called for a circle\n";
}
void Circle::view() {
cout << "Radius = " << r << endl;
}
Circle Circle::circumference() {
return 2 * M_PI * r;
}
Circle Circle::area() {
return M_PI * pow(r, 2);
}
void Circle::getArea() {
cout << "Area = " << r << " m^2";
}
void Circle::getCircum() {
cout << "Circumference = " << r << " m";
}
cylinder.h
#pragma once
#include <iostream>
#include "circle.h"
class Cylinder : public Circle {
public:
float h;
Cylinder();
Cylinder(float r, float h);
void view();
double area();
double volume(float r, float h);
void getArea();
void getVolume();
};
cylinder.cpp
#include "cylinder.h"
#include <cmath>
using namespace std;
Cylinder::Cylinder() : h(7) {
cout << "Default constructor has been called for a cylinder\n";
}
Cylinder::Cylinder(float r, float h) : Circle(r) {
this->h = h;
cout << "Constructor with parameters has been called fo a cylinder\n";
}
void Cylinder::view() {
Circle::view();
cout << "Height = " << h << endl;
}
double Cylinder::area() {
return 2 * M_PI * r * h;
}
double Cylinder::volume(float r, float h) {
return M_PI * pow(r, 2) * h;
}
void Cylinder::getArea() {
cout << "Area = " << h;
}
void Cylinder::getVolume() {
cout << "Volume = " << h;
}
main.cpp
#include <iostream>
#include "circle.h"
#include "cylinder.h"
using namespace std;
int main() {
Circle A;
A.view();
Circle A1(8);
A1.view();
Cylinder B;
B.view();
Cylinder B1(4, 6);
B1.view();
//A.area().getArea();
//cout << endl;
//A.circumference().getCircum();
//cout << endl;
//A1.area().getArea();
//cout << endl;
//A1.circumference().getCircum();
B.area().getArea();
return 0;
}
The error that I'm getting:
main.cpp: In function ‘int main()’:
main.cpp:26:14: error: request for member ‘getArea’ in ‘B.Cylinder::area()’, which is of non-class type ‘double’
26 | B.area().getArea();
| ^~~~~~~
I feel like neither my code in main() for instance B, nor my methods getArea() and getVolume() in class Cylinder, are correct. And there is probably a better approach to do the same for an object A and A1 of a Circle type, though the code I commented out actually works.
I know that this is a dumb question, and such things should be quite straightforward, but I am trying to learn and would be grateful for any advice on how I can fix this.

Answer 1

Well, the reason you are getting the error message:
main.cpp: In function ‘int main()’:
main.cpp:26:14: error: request for member ‘getArea’ in ‘B.Cylinder::area()’, which is of non-class type ‘double’
26 | B.area().getArea();
| ^~~~~~~
Is because you are basically doing this:
auto _ = B.area();
So here, _ deduces to be a double, and then you do:
_.getArea();
You are trying to access a member function from a double, and double doesn't have any member functions.
You probably meant to do this instead:
auto x = B.area();
B.h = x;
B.GetArea();
This assigns the area of B.area() to a variable x, and assigns x to B.h. B's member function then gets called and outputs the area.

Answer 2

In your getArea() function, instead of saying:
cout << "Area = " << endl;
Just say:
cout << "Area = " << area() << endl;
Then in your main.cpp, just call B.getArea().
Hope this helps!