Coroutine basics (IEnumerator) in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Coroutine?

Consider this Unity Coroutine code snippet. What will be printed to the console?

Unity

IEnumerator PrintNumbers()
{
    Debug.Log("Start");
    yield return new WaitForSeconds(1);
    Debug.Log("Middle");
    yield return new WaitForSeconds(1);
    Debug.Log("End");
}

// Assume this Coroutine is started once at time 0.

A Only "Start" is printed, then Coroutine stops

B "Start", "Middle", and "End" all printed immediately

C "Start" immediately, then "Middle" after 1 second, then "End" after 2 seconds

D "Start" after 1 second, "Middle" after 2 seconds, "End" after 3 seconds

💡 Hint

Remember that yield return new WaitForSeconds(1) pauses the Coroutine for 1 second before continuing.

The Coroutine prints "Start" immediately, then waits 1 second before printing "Middle", then waits another second before printing "End".

🧠 Conceptual

intermediate

What happens if you call StopCoroutine on a running Coroutine?

In Unity, if you start a Coroutine and then call StopCoroutine on it before it finishes, what will happen?

A The Coroutine immediately stops and no further code inside it runs

B The Coroutine finishes running all remaining code instantly

C The Coroutine pauses but resumes after some time automatically

D Nothing happens; the Coroutine continues running normally

💡 Hint

Think about what stopping a Coroutine means in Unity.

Calling StopCoroutine immediately halts the Coroutine. No further code inside it will execute.

🔧 Debug

advanced

Why does this Coroutine never print "Done"?

Look at this Coroutine code. It never prints "Done". Why?

Unity

IEnumerator WaitAndPrint()
{
    yield return new WaitForSeconds(2);
    yield return null;
    Debug.Log("Done");
}

// Coroutine started once.

A Because <code>yield return null</code> pauses only one frame, so "Done" should print

B Because the Coroutine is never started properly

C Because <code>yield return null</code> causes the Coroutine to restart endlessly

D Because the Coroutine is stopped externally before reaching "Done"

💡 Hint

Think about what yield return null does in a Coroutine.

yield return null waits one frame, then continues. So "Done" will print after 2 seconds plus one frame.

📝 Syntax

advanced

Which option correctly defines a Coroutine method?

Which of these method signatures is valid for a Coroutine in Unity?

A public int MyCoroutine()

B public void MyCoroutine()

C public async Task MyCoroutine()

D public IEnumerator MyCoroutine()

💡 Hint

Remember that Coroutines must return IEnumerator.

Coroutines in Unity must return IEnumerator. Other return types are invalid for Coroutines.

🚀 Application

expert

How many times will "Tick" print in this Coroutine?

Consider this Coroutine that prints "Tick" every 0.5 seconds for 3 seconds total. How many times will "Tick" print?

Unity

IEnumerator TickCoroutine()
{
    float elapsed = 0f;
    while (elapsed < 3f)
    {
        Debug.Log("Tick");
        yield return new WaitForSeconds(0.5f);
        elapsed += 0.5f;
    }
}

// Coroutine started once.

A 5 times

B 6 times

C 7 times

D 3 times

💡 Hint

Count how many 0.5 second intervals fit into 3 seconds.

The loop runs while elapsed is less than 3. It increments elapsed by 0.5 each time, so it runs 6 times, printing "Tick" each time.