c# how is "create array class from class that has array variable"?

hi i wrote a code i c# and i create stuct array from struct that has a array but i have a error on Visual Studio.

my code:

public class o {

public int[] a = new int[5];

public int[] b = new int[5];

public int[] c = new int[5];

}

public class b {

public o[] yy = new o[5];

}

public Form1()

{

InitializeComponent();

}

private void Form1_Load(object sender, EventArgs e)

{

b[] oo = new b[5];

oo[0].yy[0].a[1] = 4;

}

i have error:

Object reference not set to an instance of an object.

how i can solution this problem ?

best regard.

It's because you are using an uninitialized array.
oo[0] is null, that is why you were encountering an "Object reference not set to an instance of an object" error. You need to initialize your class arrays first before usage.

class b
    {
        public o[] yy = new o[5];

        public b()
        {
            // initialize the array variables
            for (int index=0; index            {
                yy[index] = new o();
            }
        }
    }

private void Form1_Load(object sender, EventArgs e)
{

    b[] oo = new b[5];

    // always remember that you have to initialize your class array before you'll be able to use it
    for (int index = 0; index < oo.Length; index++)
    {
        oo[index] = new b();
    }

    oo[0].yy[0].a[1] = 4;
}