as @BartoszKP commented mytext[i]
is null and you will get an exception when you set Text
property of null object , try with below
if (myvar == null)
{
mytext[i] = new TextBox();
mytext[i].Text = Convert.ToString(inglist.Items[inglist.SelectedIndex]);
}
OR
TextBox[] mytext =Enumerable.Range(0,8).Select(x=> new TextBox()).ToArray();