C# Scripting Basics in Unity

# CHAPTER 5

C# Scripting Basics in Unity #

1. Introduction #

2. Learning Objectives #

• Create and attach C# scripts to GameObjects.

• Understand the using tags and the MonoBehaviour class.

• Declare variables (int, float, bool, string).

• Differentiate between the Start() and Update() methods.

• Write custom functions to organize code.

• Print debugging messages to the Unity Console.

3. Creating and Attaching a Script #

1. 1. In the Project window, right-click -> Create -> C# Script.

1. 2. CRITICAL: Name it immediately (e.g., PlayerLogic) and press Enter. Do not click away! The file name must exactly match the class name inside the code.

1. 3. Double-click the script to open it in Visual Studio.

1. 4. To make the script run, drag the script file from the Project window and drop it onto a GameObject (like your Player) in the Hierarchy. It is now a Component!

4. Anatomy of a Unity Script #

using UnityEngine; // Tells the script to use Unity's built-in code library

// The class name MUST match the file name!
// ": MonoBehaviour" means this script can be attached to a GameObject.
public class PlayerLogic : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

5. Variables (Storing Data) #

• int: Whole numbers (1, 5, -10). Good for health or score.

• float: Decimal numbers (3.14f, 5.0f). Always end with an 'f'. Good for speed or time.

• bool: True or False. Good for isDead or isGrounded.

• string: Text ("Hello World"). Good for player names.

*Making a variable public allows you to change its value directly in the Unity Inspector without opening the code!*

public int playerHealth = 100;
public float moveSpeed = 5.5f;
public bool hasKey = false;

6. Start() vs. Update() #

• void Start(): Runs exactly ONCE, the moment the object is spawned (or the game starts). Use this to set up starting values or find other objects.

• void Update(): Runs continuously, once every single frame (e.g., 60 times a second). Use this to check for player input or move objects.

7. Functions (Organizing Code) #

void Update()
{
    if (playerHealth <= 0)
    {
        Die(); // Call the custom function
    }
}

// A custom function
void Die()
{
    Debug.Log("Player has died!");
    Destroy(gameObject); // Deletes the object from the game
}

8. Debugging to the Console #

9. Best Practices #

• Use [SerializeField] instead of public: Making a variable public exposes it in the Inspector, but it also allows any other script in the game to change it. A better practice is to make it private (so other scripts can't break it), but add [SerializeField] above it. This magical tag forces Unity to show it in the Inspector anyway!

10. Common Mistakes #

• The Class Name Mismatch: If you create a script, click away, and then rename the file to EnemyAI, the code inside will still say public class NewBehaviourScript. Unity will throw a massive error and refuse to let you attach the script. The file name and the class name MUST be identical!

11. Mini Project: The Console Calculator #

1. 1. Create a script named Calculator. Attach it to the Main Camera.

1. 2. Open it and write the following code:

using UnityEngine;

public class Calculator : MonoBehaviour
{
    public int damage = 15;
    public int currentHealth = 100;

    void Start()
    {
        Debug.Log("Game Started. Health is: " + currentHealth);
        TakeDamage(); // Call the function once
    }

    void TakeDamage()
    {
        currentHealth = currentHealth - damage;
        Debug.Log("Ouch! Took damage. New Health: " + currentHealth);
    }
}

1. 3. Press Play in Unity and watch the Console output!

12. Practice Exercises #

1. 1. What does the f at the end of 5.5f represent in C#?

1. 2. Why is it dangerous to put a command like "Spawn an Enemy" directly inside the Update() loop without an if statement?

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain the inheritance requirement for a C# class to be attached to a Unity GameObject as a Component. What base class must it inherit from?

• Q: Contrast the execution frequency of the Start() method versus the Update() method. Give an example of code that belongs in each.

• Q: A junior developer renames a C# script file in the Unity Project window from Bullet to Missile. Suddenly, the script won't compile, and Unity throws an error. Why did this happen, and how do you fix it?

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #