Inheritance

Unity components inherit from MonoBehaviour and that is what makes the code that we are creating work inside Unity and not in other C# applications. For beginners to Unity, studying C# inheritance isn't a subject you need to learn in any great detail, but you do need to know that each Unity script uses inheritance. We see the code in every script that will be attached to a GameObject. In variableScript, the code is on line 4:

public class variableScript : MonoBehaviour 

The colon and the last word of this code mean that the variableScript class is inheriting behaviors from the MonoBehaviour class. This simply means that the MonoBehaviour class is making a few of its variables and methods available to the variableScript class. It's no coincidence that the variables and methods inherited look like some of the code that we saw in the Unity Scripting Reference.

The following are the two inherited behaviors in the variableScript class:

Line 10: void Start () 
Line 15: void Update () 

You don't have to call these methods; Unity calls them behind the scenes. So, the code that you place in these methods gets executed automatically.