Explore classes and object-oriented programming concepts like information-hiding, inheritance, and polymorphism.

Become a C++ Programmer

In this module, we’ll dive into understanding the time-honored technique for implementing complex applications using user-defined classes. Moreover, we’ll discuss classes and objects, then build up to the high-level topics including inheritance and polymorphism.

Throughout the module, we’ll work with OOP for C++, with illustrations, exercises, quizzes, and hands-on challenges. By end of this module, we’ll have an understanding of classes and objects' behavior and be able to easily create simple, efficient, reusable, and secure code.

Object-oriented Programming in C++

This program is an example of __composition__. The `Event` class holds `Date` and `Time` objects that have no utility or lifetime outside of the `Event` object that contains them. Let's look at the implementation:

#include <iostream>
#include <string>
#include "date.h"
#include "time.h"
class Event {
    private:
        std::string title;
        Date d;
        Time t;
    public:
        Event(std::string title, unsigned int month, unsigned int day, unsigned int year, unsigned int hours, unsigned int minutes, unsigned int seconds) {
            Event::title = title;
            d.setDate(month, day, year);
            t.setTime(hours, minutes, seconds);
        }
        void display() {
            std::string date, time;
            d.toString(date);
            t.toString(time);
            std::cout << title + " occurs on " + date + " at " + time << std::endl;
        }
};

#include <string>
class Date {
    private:
        unsigned int day;
        unsigned int month;
        unsigned int year;
    public:
        Date(unsigned int m, unsigned int d, unsigned int y) {
            setDate(m, d, y);
        }

        Date() {
            setDate(1, 1, 1900);
        }

        void setDate(unsigned int m, unsigned int d, unsigned int y) {
            month = m;
            day = d;
            year = y;
        }

        void toString(std::string& s) {
            if (month < 10)
                s = "0";
            s += std::to_string(month);
            s += "-";
            if (day < 10)
                s += "0";
            s += std::to_string(day);
            s += "-";
            s += std::to_string(year);
        }
};

#include <string>

class Time {
    private:
        unsigned int hours;
        unsigned int minutes;
        unsigned int seconds;
    public:
        Time(unsigned int h, unsigned int m, unsigned int s) { 
            setTime(h, m, s);
        }

        Time() {
            setTime(0, 0, 0);
        }

        void setTime(unsigned int h, unsigned int m, unsigned int s) {
            hours = h;
            minutes = m;
            seconds = s;
        }

        void toString(std::string& s) {
            if ( hours < 10 )
                s = "0";
            s += std::to_string(hours);
            s += ":";
            if (minutes < 10)
                s += "0";    
            s += std::to_string(minutes);
            s += ":";
            if (seconds < 10)
                s += "0";
            s += std::to_string(seconds);
        }
};

#include "event.h"

int main() {
  Event e("Course Launch", 5, 15, 2021, 12, 30, 0);
  e.display();
}

The file `event.h` is where the exciting stuff is happening. Let's look at the constructor on lines 11 - 15, first.

On line 12, we are setting the `title` member variable to the value of the `title` argument. To disambiguate the identical variable names, we are using the scope resolution operator.

On line 13 and 14, we are invoking the `setDate()` and `setTime()` functions, respectively to set the proper values for the date and time of the event.

Then comes the `display()` method on lines 16 - 21. We first declare two `string` variables on line 17 to hold a text version of date and time values so that we can easily display them. We request the `Date` class object to write its value as a `string` in the `date` variable on line 18. Similarly, we ask the `Time` class object to write its value as a `string` in the `time` variable on line 19. Then, we concatenate these `string` variables with the literal `string` values (required to be part of the message) and displayed the result on the screen on line 20.

Introduction

Classes

Data Hiding

Inheritance

Polymorphism

Composition, Aggregation and Association

Conclusion

Solution Review: Event Data