Start and Update methods in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Unity script?

Consider this Unity C# script attached to a GameObject. What will be printed to the console when the game starts and after 2 seconds?

Unity

using UnityEngine;

public class TestScript : MonoBehaviour
{
    void Start()
    {
        Debug.Log("Start called");
    }

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

A "Update called" repeatedly, but "Start called" never appears

B "Start called" once, then "Update called" repeatedly every frame

C "Start called" once, then "Update called" once

D No output at all

💡 Hint

Remember that Start runs once before the first frame, and Update runs every frame if the script is enabled.

The Start method runs once when the script is enabled. The Update method runs every frame, but here it disables the script after the first call, so Update runs only once.

🧠 Conceptual

intermediate

When is the Start method called in Unity?

Choose the correct statement about when the Start method is called in a Unity script.

A Once before the first frame update, if the script is enabled

B Every frame before <code>Update</code> is called

C Only when the script is disabled

D After every <code>Update</code> call

💡 Hint

Think about initialization timing in Unity scripts.

Start runs once before the first frame update, but only if the script component is enabled.

❓ Predict Output

advanced

What happens if you disable a GameObject in Start and try to use Update?

What will be the output of this script attached to a GameObject?

Unity

using UnityEngine;

public class DisableInStart : MonoBehaviour
{
    void Start()
    {
        Debug.Log("Start running");
        gameObject.SetActive(false);
    }

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

A No output at all

B "Start running" and "Update running" printed repeatedly

C Only "Update running" printed repeatedly

D "Start running" printed once, no "Update running" printed

💡 Hint

Think about what happens when a GameObject is deactivated.

When the GameObject is deactivated in Start, Update will not run because the object is inactive.

🔧 Debug

advanced

Why does this Update method never run?

Look at this script. Why does the Update method never print anything?

Unity

using UnityEngine;

public class NeverUpdate : MonoBehaviour
{
    void Start()
    {
        enabled = false;
        Debug.Log("Start called");
    }

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

A Because <code>Update</code> is private and cannot run

B Because <code>enabled</code> is set to false in <code>Start</code>, disabling the script before <code>Update</code> can run

C Because <code>Start</code> disables the GameObject

D Because <code>Update</code> requires a parameter

💡 Hint

Check what disabling the script component does.

Setting enabled = false disables the script component, so Update will not be called.

🚀 Application

expert

How to run code exactly once after 3 seconds using Start and Update?

You want to print "Hello after 3 seconds" exactly once, 3 seconds after the game starts. Which code snippet achieves this?

A

float timer = 0f;
void Update() {
  timer += Time.deltaTime;
  if (timer >= 3f) {
    Debug.Log("Hello after 3 seconds");
    enabled = false;
  }
}

B

void Start() {
  InvokeRepeating("PrintHello", 3f, 3f);
}
void PrintHello() {
  Debug.Log("Hello after 3 seconds");
}

C

void Start() {
  Debug.Log("Hello after 3 seconds");
  StartCoroutine(WaitAndPrint());
}
IEnumerator WaitAndPrint() {
  yield return new WaitForSeconds(3f);
  Debug.Log("Hello after 3 seconds");
}

D

void Update() {
  if (Time.time == 3f) {
    Debug.Log("Hello after 3 seconds");
  }
}

💡 Hint

Think about how to measure time passing in Update and stop after printing once.

Option A uses a timer variable incremented by Time.deltaTime each frame, prints after 3 seconds, then disables the script to stop further calls.

Option A repeats every 3 seconds, not once. Option A is invalid because Start is not a coroutine here. Option A compares floats exactly, which is unreliable.