Question

I came a cross some difficulty with my object.
Im trying to have an array of object (Question) that I’ve created:

public class Question
{
    public int id = 0;
    public string question = string.Empty;

    public string a1 = string.Empty;
    public string a2 = string.Empty;
    public string a3 = string.Empty;
    public string a4 = string.Empty;

    public int Tanswer = 0;

}

and Now Im trying to set some values in it like this :

Question[] arr = new Question[4];

    Random rnd = new Random();

    int i = 0;
    int temp = 0;
    bool ok = false;

    while (i < 3)
    {
        temp = rnd.Next(0, Int32.Parse(dt_count.Rows[0][0].ToString()) - 1);
        for (int j = 0; j < arr.Length; j++)
        {
            arr[j].id = Int32.Parse(dt_q_notMust.Rows[temp][0].ToString());  // ID
            arr[j].question = dt_q_notMust.Rows[temp][1].ToString();  // Question
            arr[j].a1 = dt_q_notMust.Rows[temp][2].ToString();  // A1
            arr[j].a2 = dt_q_notMust.Rows[temp][3].ToString();   // A2
            arr[j].a3 = dt_q_notMust.Rows[temp][4].ToString();  // A3
            arr[j].a4 = dt_q_notMust.Rows[temp][5].ToString();  // A4
            arr[j].Tanswer = Int32.Parse(dt_q_notMust.Rows[temp][6].ToString());  // True Answer (int).

            if (arr[j].id != temp)
            {
                ok = true;

            }
        }

        if (ok)
        {
            i++;
        }
    }

and its write an error for some reason, like I’ve been never initialize it :

Object reference not set to an instance of an object.

but I did wrote the :

Question[] arr = new Question[4];

so I wonder whats the problem is ?

Thanks!

Answer 1

You’ve initialised arr as a new array, but all of its elements are still null. You need to initialise each item before you access it:

arr[j] = new Question();
arr[j].id = Int32.Parse(dt_q_notMust.Rows[temp][0].ToString());
...