Introduction to coding

About this tutorial

The purpose of this tutorial is to introduce how coding works, with the C++ language here, by creating and explaining, step by step, the code of a small 2D game. In other words, the goal is to provide an overview of programming with the C++ language. If you wish to learn to code or to improve your C++ skills, you will find, at the end of this tutorial, a link to a free and in-depth C++ course.

The code of the game and some coding concepts will be explained, but keep in mind that this is an introduction and not a course. After this tutorial, you should have an idea of how coding works, but if you want to really understand it, you should follow a course.

Some theory

Before getting into the creation of the game, let us have a very quick look at the C++ language.

Variables

A variable is simply a memory space which has a name. It is used to store data.

The following line of code defines (creates) a variable of type 'int' (A type able to hold integer numbers) and named 'var':

C++:

int var;

Here, we set its value to 33:

C++:

var = 33;

We set its value to its own value plus 10 (43):

C++:

var = var + 10;

Functions

A function is a group of instructions that has been assigned a name. It can return a value, which can be seen as its result.
Here is the definition (creation) of a function:

C++:

int func(int arg)
{
    return arg;
}

Some points to note:

The first 'int' indicates that the function returns a value of type 'int' (An integer number).
The name of the function is 'func'.
It takes a parameter of type 'int' and referred to as 'arg'.
The instructions of a function are located inside its braces. Here, its only instruction has the effect of returning the value of the parameter it received.

Note that, in C++, all instructions are ended by a semicolon.

We can call the function defined above, like such:

C++:

func(46);

Calling a function means executing the instructions inside it. In the function call from above, the argument (parameter) 'arg' will receive (Be assigned with) the value 46. If there was many arguments, we would have to separate them with commas.

The main function

Here is a minimal C++ code that does... nothing.

C++:

int main()
{
    return 0;
}

The code above defines the main function of the program. When a program is launched, the operating calls its main function to start it.

The main function returns the error code (number) 0 to the operating system, indicating that the program ended successfully.

SFML

The C++ language does not directly provide tools to display graphics. To do so, we must use sets of tools called libraries. This tutorial uses the library SFML, which provides a multitude of functionalities, the drawing of pictures and the management of windows included.

Once a library is installed, we must write a line of code to include it to the project, so it can be used within the code. The following line of code includes the graphical functionalities of SFML:

C++:

#include <SFML/Graphics.hpp>

Objects

A class is a special type of variable. A class is made up of variables (Called members) and functions (Called methods) that execute tasks such as modifying its members. A variable of a class type is called an object.

If we consider that the following line of code defines (creates) an object:

C++:

Window win;

And that the class 'Window' possesses a method called 'open' and a member variable called title, then, we can call (execute) its method 'open' like such:

C++:

win.open();

And access its member 'title' like that:

C++:

win.title;

When an object is defined, a function, called the constructor, is called. Its purpose is to initialize the object. If it takes arguments, we may give them inside parentheses following the name of the object, at its creation.

C++:

Window win(arg1, arg2, arg3);

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Introduction to coding - 1. Introduction