Explanation about Constructors and Inheritence

Question

Recently, I started working with classes and, today, class inheritance. I created a simple program to expand my perception of inheritance. The program calculates the average grade of a class. I understand the vast majority of the code I have written, but there are some exceptions (listed below the code). Any and all help would be appreciated.

Code

#include "stdafx.h"
#include <iostream>

using namespace std;

class CAverage {
    private:
        double VSubCount, VAverage, VMark, VSum, VNum;
    public: CAverage(int); // Constructor.
        void MTake_action() {
            MAsk_input(); // Calls the method “MAsk_input()“ within this class.
            MCalculate_average(); // Calls the method “MCalculate_average()“ within 
                                  // this class.
            MPrint_result(); // Calls the method “MPrint_result()“ within this class.
        }

        void MCalculate_average() {
            VAverage = VSum / VNum;
        }

        void MAsk_input() {
            VSum = 0;
            VNum = 0;
            int VNumber;
            for (int i = 0; i < VSubCount; i++) {
                cout << "Enter your " << i + 1 << " mark: ";
                cin >> VNumber;
                if (VNumber > 0) {
                    VMark = VNumber;
                    VSum += VMark;
                    VNum++;
                }
            }
        }

        void MPrint_result()
        {
            system("cls");

            if (((VSum / 3) <= 0) || ((VSum / 3) > 10)) {
                cout << "Incorrect input." << endl;
            } else {
                cout << "Average: " << VAverage << endl;
            }
        }
};

// Creates a child class and makes that this class could view/get public methods,
// variables, etc of “CAverage“.
class CGroup : public CAverage {
    private:
        int VClassMembers;
        void MAsk_input() {
            for (int i = 0; i < VClassMembers; i++) {
                system("cls");

                cout << "[" << i + 1 << " student]" << endl;

                CAverage::MAsk_input(); // Calls the method “MAsk_input()“ within
                                        // the parent class (“CAverage“).
            }
        }
    public: CGroup(int, int);
        void MTake_action() {
            MAsk_input(); // Calls the method “MAsk_input()“ within this class.
            CAverage::MCalculate_average(); // Calls the method “MCalculate_average()“
                                            // within the parent class (“CAverage“).
            CAverage::MPrint_result(); // Calls the method “MPrint_result()“ within the
                                       // parent class (“CAverage“).
        }
};

CAverage::CAverage(int VSubjectCount) {
    VSubCount = VSubjectCount;
}

CGroup::CGroup(int VOther, int VInteger) : CAverage(VOther) {
    VClassMembers = VInteger;
}

int main() {
    CGroup avg(2, 5); // Creates an object, named “avg“.

    avg.MTake_action(); // Calls the child classes' method “MTake_action()“.

    return 0;
}

So, how would one explain these parts?

CAverage::CAverage(int VSubjectCount) {
    VSubCount = VSubjectCount;
}

CGroup::CGroup(int VOther, int VInteger) : CAverage(VOther) {
    VClassMembers = VInteger;
}

I think that this

CAverage(int);

and this

CGroup(int, int);

call the constructors? Or, are they themselves the constructors?

And, are all of the comments, made by me, correct?

Answer 1

I think that this

CAverage(int);

and this

CGroup(int, int);

call the constructors? Or, are they themselves the constructors?

Your second presumption is correct, both are constructors.

CAverage::CAverage(int VSubjectCount) {
    VSubCount = VSubjectCount;
}

This snippet initializes the variable VSubCount within the superclass.

CGroup::CGroup(int VOther, int VInteger) : CAverage(VOther) {
    VClassMembers = VInteger;
}

This is a little more complex, and shows key concepts of inheritance.

: CAverage(VOther)

Is calling the parent constructor, to initialize the private member VSubCount, in CAverage, since CGroup cannot access it.

VClassMembers = VInteger;

initializes the member VClassMembers in the subclass. Otherwise, your comments are correct.