Introduction to Classes in C++

Declaring a Class

After defining a class, you can declare it as a variable using the same syntax we have used for any other variable. A class is declared using its name followed by a name for the defined variable and ending with a semi-colon. For example, our ShoeBox class can be declared as follows:

ShoeBox Shake;

When an object has been declared, you can access any of its members using the member access operator “.”. First, type the name of the object variable, followed by a period, followed by the name of the member you want to access. For example, to access the member Length of the above class, you would write:

Shake.Length;

Using this syntax, you can display the value of a class member:

cout << Shake.Length;

or you can request its value from the user, using the cin operator. Here is an example:

cin >> Shake.Lengh;

Using the

cout

extractor to display the values of the object members, our program could be as follows:

#include <iostream>

#include <string>

using namespace std;

c lass ShoeBox {
    public: double Length,
    Width,
    Height;
    string Color;
    private: float ShoeSize;
};

int main() {
    ShoeBox Shake; // Display the characteristics of the shoe box

    cout << "Characteristics of this shoe box";
    cout << "\n\tLength = " << Shake.Length <<
        "\n\tWidth = " << Shake.Width <<
        "\n\tHeight = " << Shake.Height <<
        "\n\tVolume = " << Shake.Length * Shake.Width * Shake.Height <<
        "\n\tColor = " << Shake.Color <<
        "\n\tSize = " << Shake.ShoeSize <<
        "\n\n";

    return 0;
}

At this time, because of trying to access a private member, the program would produce the following error

[C++ Error] Unit1.cpp(30): E2247 ‘ShoeBox::TShoeSize’ is not accessible

Even if you change the ShoeSize member access from private to public, the program would render unpredictable results because the members have not been given appropriate values:

Characteristics of this shoe box Length = 0 Width = 1.79571e-307 Height = 4.17266e-315 Volume = 0 Color = Size = 3.58732e-43

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