Small Steps V — Making Your Own Types

Grouping data and operations

Group data and operations.

What you will learn

A class groups data with operations on that data. An object is an actual instance of its type. This lesson introduces the idea that you can make such tools yourself.

Try it

class Counter
{
public:
    void add_one()
    {
        value = value + 1;
    }

    int get_value()
    {
        return value;
    }

private:
    int value = 0;
};

void small_main()
{
    Counter counter;

    counter.add_one();
    counter.add_one();

    print(counter.get_value());
}

A Counter object holds its counted value. Calling add_one twice and reading get_value() gives 2.

public exposes a part to users; private prevents direct access from outside. You have already used String and Window as objects with data and related operations. Constructors and inheritance are beyond this lesson.

Exercise

Add a public reset() to Counter that sets its value to 0, and check that it works.

class Counter
{
public:
    void add_one()
    {
        value = value + 1;
    }

    void reset()
    {
        // reset value.
    }

    int get_value()
    {
        return value;
    }

private:
    int value = 0;
};

void small_main()
{
    Counter counter;
    counter.add_one();
    counter.add_one();
    counter.reset();
    print(counter.get_value());
}

Hint

Assign 0 to the private value inside reset.

class Counter
{
public:
    void add_one()
    {
        value = value + 1;
    }

    void reset()
    {
        value = 0;
    }

    int get_value()
    {
        return value;
    }

private:
    int value = 0;
};

void small_main()
{
    Counter counter;
    counter.add_one();
    counter.add_one();
    counter.reset();
    print(counter.get_value());
}