The structure of a C# script

Today, let's examine a script, one of the main building blocks of behavior in Unity. Open Unity and double-click the Move script we created. Visual Studio Code should open shortly afterward.

using directives

At the top, you will see lines beginning with:

using

These directives make names from other namespaces available in the file. The original describes this as using features from libraries: a useful introductory idea, though a using directive itself does not install or load a library.

The script class

The original text then shows this class declaration:

public class Move : MonoBehavior

The class is where the script's members and behavior live. Make sure its name matches the script asset. If the file is named Move.cs, the class should be named Move, rather than a default name left from creating a new script.

Editorial correction: Unity's base-class name is MonoBehaviour, with a u. The source's typed excerpt above misspells it as MonoBehavior. The intended declaration is public class Move : MonoBehaviour.

Start and Update

Next come methods. A function or method groups behavior that runs when called. Two common Unity lifecycle methods are:

void Start()
void Update()

Start() runs once before the component's first update when it becomes active. Update() runs once per rendered frame while the component is enabled.

Which runs first? Start.

Start is commonly used to initialize values, obtain references, or do one-time setup. Update commonly handles ongoing behavior such as frame-by-frame input or movement. Physics work has its own timing considerations, which become relevant later.

That is the basic script structure. Next, we will finally write movement code.