How to solve these errors with rand?

Question

C++ / C#

Have a question how to fix it? <

private float textimer;
    public float time = 3f;
    public GameObject govno;
    private bool provoda = true;
    public float s;
    public float r;


    float res = rand.Next(array.Length);

    private Vector3[] coords = new Vector3[3] { new Vector3(-4.39f, 5.83f, 90.4f), new Vector3(-1.7f, 5.83f, 90.4f), new Vector3(0.52f, 5.83f, 90.4f) };

    IEnumerator Da()
    {
        while (provoda==true)
        {
            int randomNumber = Random.Range(0, coords.Length);
            Instantiate(Object, coords[randomNumber]);
        }
    }

Answer 1

As well as problems with
float res = blabla.Trututu(array.Length);
No you have none rand.