Countdown timer using Coroutine in Unity

Countdown

private float currCountdownValue = 0;

public IEnumerator StartCountdown(float countdownValue = 10) {
    currCountdownValue = countdownValue;
    while (currCountdownValue > 0) {
        Debug.Log("Countdown: " + currCountdownValue);
        yield return new WaitForSeconds(1.0f);
        currCountdownValue--;
    }
}

// to use
StartCoroutine(StartCountdown());
// or 
StartCoroutine(StartCountdown(10));