How to make waves of enemys spawn after few seconds.

Questions & Answers
1

Hi, I picked up unity less than week ago so I don’t realy know what’s wrong with this code. I’ve read that you can’t use WaitForSeconds();in Update but I don’t know why and I don’t know how to do it otherwise. Can somebody help me how should I do it?

public class Spawning : MonoBehaviour
{
    public GameObject zombiePrefab;
    int randomSpawnZone;
    float randomPositionX, randomPositionY;
    Vector3 spawnPosition;
    public float enemySpawned = 5f;
    public float enemysToKill = 5;
    public float enemyAddedEveryRound = 1;
    
    void Start ()
    {
        for (int i = 0; i < enemySpawned; i++)
        {
            SpawnNewEnemy();
        }
    }
    
    void Update ()
    {
        EnemyWaveSpawner();
    }
    
    IEnumerator Wait()
    {
        yield return new WaitForSeconds(3);
    }
    
    void SpawnNewEnemy()
    {
        randomSpawnZone = Random.Range(0, 4);

        switch (randomSpawnZone)
        {
            case 0:
                randomPositionX = Random.Range(-10f, 10f);
                randomPositionY = Random.Range(-6f, -5f);
                break;
            case 1:
                randomPositionX = Random.Range(-10f, 10f);
                randomPositionY = Random.Range(5f, 6f);
                break;
            case 2:
                randomPositionX = Random.Range(10f, 11f);
                randomPositionY = Random.Range(-5f, 5f);
                break;
            default:
                randomPositionX = Random.Range(-11f, -10f);
                randomPositionY = Random.Range(-5f, 5f);
                break;
        }
        spawnPosition = new Vector3(randomPositionX, randomPositionY, 0f);
        Instantiate(zombiePrefab, spawnPosition, Quaternion.identity);
    }
    
    void EnemyWaveSpawner()
    {
        if (enemysToKill == 0)
        {
            Wait();
            enemySpawned += enemyAddedEveryRound;
            enemysToKill = enemySpawned;
            for (int i = 0; i < enemySpawned; i++)
            {
                SpawnNewEnemy();
            }
        }
    }
    
}
2

You need to write StartCoroutine(COROUTINE()); So instead of calling the Wait function like Wait(); you have to write
StartCoroutine(Wait());

You cannot write yield return new WaitForSeconds() in the update function becuse it returns void compared to your Wait function that returns an IEnumerator. I am not that knowledgeable about how coroutines actually work but here are some links if you want to learn more.