Sometimes we need to make sure that a value can never be changed. To achieve this we can declare and initialize a constant using the const keyword:

const float PI = 3.141f; 
const int PLANETS_IN_SOLAR_SYSTEM = 8; 
const int NUMBER_OF_ENEMIES = 2000; 

It is conventional to declare constants in all upper case. The value of the preceding constants can never be altered. We will see some constants in action in Chapter 4: Loops, Arrays, Switch, Enumerations, and Functions - Implementing Game Mechanics.

User-defined types are way more advanced than the types we have just seen. When we talk about user-defined types in C++ we are usually talking about classes. We briefly talked about classes and their related objects in the previous chapter. We can write code in a separate file, sometimes in two separate files. From these we will then be able to declare, initialize, and use them. We will leave how we define/create our own types until Chapter 6: Object-Oriented Programming, Classes, and SFML Views.

We can declare variables in C++ like this:

// What is the player's score? 
int playerScore; 
 
// What is the players first initial 
char playerInitial; 
 
// What is the value of pi 
float valuePi; 
 
// Is the player alive or dead? 
bool isAlive; 

Now we have declared the variables with meaningful names, we can initialize those same variables with appropriate values, like this:

playerScore = 0; 
playerInitial = 'J'; 
valuePi = 3.141f; 
isAlive = true; 

When it suits us, we can combine the declaration and initialization steps into one:

int playerScore = 0; 
char playerInitial = 'J'; 
float valuePi = 3.141f; 
bool isAlive = true; 

We have already seen examples of how we declare and initialize some SFML defined types. Because the way we can create/define these types (classes) is so flexible, the way we declare and initialize them is also highly varied. Here are a couple of reminders for declaring and initializing user-defined types, from the previous chapter.

Create an object of type VideoMode, called vm, and initialize it with two int values, 1920 and 1080:

// Create a video mode object 
VideoMode vm(1920, 1080); 

Create an object of type Texture, called textureBackground but don't do any initialization:

// Create a texture to hold a graphic on the GPU 
Texture textureBackground; 

Note that it is possible (in fact very likely) that even though we are not suggesting any specific values with which to initialize textureBackground, some variables may be set up internally. Whether or not an object needs/has the option of giving initialization values at this point is entirely dependent on how the class is coded and is almost infinitely flexible. This further suggests that when we get to write our own classes there will be some complexity. Fortunately, it also means we will have significant power to design our types/classes, so they are just what we need to make our games! Add this huge flexibility to SFML-designed classes and the potential for our games is almost limitless.

We will see a few more user-created types/classes provided by SFML in this chapter too and loads more throughout the book.