Object oriented programming (Introduction) - Article 1

Hi Folks,

Let's start off on OOP and C++. This is an introductory article for the bigger things coming in the future weeks.

What is OOP or Object oriented programming?

OOP stands for object oriented programming. C#, C++ and Java are examples of object oriented languages, where as C, Pascal are examples of procedural languages.

Modularity, extensibility, reusability and maintainability are some of the advantages of OO languages. In OOP, the software programs are organized as OBJECTs. All the entities in OOP are modelled as objects.

Suppose a problem is given, in procedural langauge like C, the problem is divided into functions (actions on data) and data are declared, whereas in C++, the problem is modelled as objects. For example, a problem on car in C will look like,

float brake;
float acceleration;

main() {
    accelerate_the_car();
        if(obstacle == true)
            apply_brake();
}

void accelerate_the_car() {

}

void apply_brake() {

}

The same in C++ would look like:

class car {
    float brake;
    float acceleration;

    public:
    void accelerate_the_car();
    void apply_brake();
};

main() {
    car ford;
    ford.accelerate_the_car();
    if(obstacle == true)
        ford.apply_brake();
}

Don't worry, I am going to explain the things in detail.

Classes & Objects

The dictionary meaning of object is as below:

Object - a material thing that can be seen and touched.

Simply put, objects have phyical existance. Imagine all the real world objects, the laptop, mobile or PC you have been using to read this blog, the car you drive, books you read, etc. Let us take example of car. All cars have properties like engine, brakes, accelerator, windows, etc. All cars exhibit behaviours - drive, accelerate, apply_brake, close_windows, etc.

A small exercise: Think of objects around you and list out their properties and behaviours.

From above, it's clear that all objects have two characteristics: properties and behaviour. As we are concerned about software and C++, let's map these. The properties are nothing but variables or data and behaviours are nothing but methods of functions acting on data.

In C++, variables and corresponding functions are bundled into objects.

So then what is a class and what is the difference between class and object? A class is nothing but CLASSification of objects. i.e., a group of related objects form a class. A class provides blue print for the object and does not have physical existence, where as we have seen that objects have physical existance.

Let me give a real world example. Ford company manufactures cars. Suppose they plan to come up with new model. They design the blue print of the car, i.e., how the car should look like, type of engine, petrol or diesel, etc, etc, etc. The same goes to the factory and using this blue print, cars are manufactured. So, this blue print forms the class for cars that are manufactured.

In C++, objects are created using the class type. In the example program shown, class car is the blue print. In main(), we made an object ford.

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