Start and Update methods in Unity

Introduction

The Start and Update methods help your game objects do things when the game begins and keep doing things every frame.

When you want to set up something once before the game runs, like setting a player's health.

When you want to check for player input continuously, like moving a character.

When you want to update the game score or timer every moment.

When you want to initialize variables or settings at the start of a scene.

When you want to animate or move objects smoothly during the game.

Syntax

Unity

void Start() {
    // code here runs once at the beginning
}

void Update() {
    // code here runs every frame
}

Start runs once before the first frame.

Update runs many times per second, once every frame.

Examples

This prints a message once at the start, then prints every frame.

Unity

void Start() {
    Debug.Log("Game started!");
}

void Update() {
    Debug.Log("Frame updated");
}

Sets player health once, then checks every frame if space is pressed to jump.

Unity

int playerHealth;

void Start() {
    playerHealth = 100;
}

void Update() {
    if (Input.GetKeyDown(KeyCode.Space)) {
        Jump();
    }
}

Sample Program

This program prints a message once when the game starts. Then every second (assuming 60 frames per second), it prints how many seconds have passed.

Unity

using UnityEngine;

public class Example : MonoBehaviour {
    int counter = 0;

    void Start() {
        Debug.Log("Start method called");
    }

    void Update() {
        counter++;
        if (counter % 60 == 0) {
            Debug.Log($"Update called {counter / 60} seconds");
        }
    }
}

Important Notes

Start is good for setup tasks.

Update is good for things that change over time or need checking often.

Too much work in Update can slow your game, so keep it simple.

Summary

Start runs once at the beginning.

Update runs every frame to keep things moving.

Use them to control when and how your game objects act.

Practice

1. What is the main purpose of the Start() method in a Unity script?

easy

A. It runs every frame to update game logic.

B. It runs once at the beginning when the script is enabled.

C. It handles user input events.

D. It is used to draw graphics on the screen.

Solution

1. Step 1: Understand the role of Start()

   The Start() method is called once when the script first runs, usually at the beginning of the game or when the object is enabled.

2. Step 2: Compare with Update()

   Unlike Update(), which runs every frame, Start() only runs once to initialize things.

3. Final Answer:

   It runs once at the beginning when the script is enabled. -> Option B

4. Quick Check:

   Start() runs once = A [OK]

Hint: Start() runs once at start, Update() runs every frame [OK]

Common Mistakes:

• Confusing Start() with Update()
• Thinking Start() runs multiple times
• Assuming Start() handles input every frame

2. Which of the following is the correct syntax for the Update() method in a Unity C# script?

easy

A. void Update() { }

B. public void update() { }

C. private int Update() { return 0; }

D. void update() { }

Solution

1. Step 1: Recall Unity method syntax

   The Update() method must be void and have no parameters. It is usually declared as void Update().

2. Step 2: Check method name casing and return type

   Unity requires exact casing: Update() with capital U. It should not return a value.

3. Final Answer:

   void Update() { } -> Option A

4. Quick Check:

   Correct syntax is void Update() [OK]

Hint: Update() must be void and capital U [OK]

Common Mistakes:

• Using lowercase 'update()'
• Adding return type other than void
• Making Update() public or private unnecessarily

3. Consider this Unity C# script attached to a GameObject:

int counter = 0;

void Start() {
    counter = 5;
}

void Update() {
    counter++;
    Debug.Log(counter);
}

What will be printed to the console during the first two frames after the game starts?

medium

A. 5 then 6

B. 0 then 1

C. 6 then 7

D. 1 then 2

Solution

1. Step 1: Analyze Start() initialization

   At the start, counter is set to 5 once by Start().

2. Step 2: Analyze Update() increments and logs

   On the first frame, Update() runs, increments counter to 6, then logs 6. On the second frame, it increments to 7 and logs 7.

3. Final Answer:

   6 then 7 -> Option C

4. Quick Check:

   Start sets 5, Update adds 1 before log [OK]

Hint: Start sets initial value, Update increments before logging [OK]

Common Mistakes:

• Assuming counter logs before increment
• Thinking Start() runs every frame
• Confusing initial counter value

4. This script is attached to a GameObject:

void Start() {
    Debug.Log("Start called");
}

void Update() {
    Debug.Log("Update called");
}

Why might "Start called" never appear in the console?

medium

A. The script is disabled or the GameObject is inactive.

B. Update() is called before Start(), so Start() is skipped.

C. Debug.Log only works inside Update().

D. Start() must return a value to run.

Solution

1. Step 1: Understand when Start() runs

   Start() runs once when the script is enabled and the GameObject is active.

2. Step 2: Identify why Start() might not run

   If the script component is disabled or the GameObject is inactive, Start() will not be called, so no log appears.

3. Final Answer:

   The script is disabled or the GameObject is inactive. -> Option A

4. Quick Check:

   Start() runs only if enabled and active [OK]

Hint: Start() runs only if script and object are active [OK]

Common Mistakes:

• Thinking Update() runs before Start()
• Believing Debug.Log only works in Update()
• Expecting Start() to return a value

5. You want to create a Unity script that moves a GameObject up by 1 unit every second, but only after an initial 3-second delay. Which approach correctly uses Start() and Update() to achieve this?

hard

A. Use Update() to set the timer and move the object immediately.

B. Move the object up by 1 unit inside Start() and do nothing in Update().

C. Move the object up by 1 unit every frame inside Start().

D. Use Start() to set a timer start time, then in Update() move the object if 3 seconds passed.

Solution

1. Step 1: Use Start() to record start time

   In Start(), save the current time as a reference point for the delay.

2. Step 2: Use Update() to check elapsed time and move

   In Update(), check if 3 seconds have passed since start time; if yes, move the object up by 1 unit per second.

3. Final Answer:

   Use Start() to set a timer start time, then in Update() move the object if 3 seconds passed. -> Option D

4. Quick Check:

   Start() sets timer, Update() moves after delay [OK]

Hint: Start() sets delay start, Update() moves after delay [OK]

Common Mistakes:

• Moving object only once in Start()
• Moving object every frame without delay
• Trying to set timer inside Update() only