private void Delete_Click(object sender, EventArgs e)
{
clChecked = new CourseCollection();
for (int i = 0; i < checkedListBox1.Items.Count; i++)
{
if (checkedListBox1.GetItemChecked(i))
{
clChecked.Add(courses[i]);
checkedListBox1.Items.RemoveAt(i);
}
}
CourseDAL.DeleteSomeids(clChecked);
UpdateCombobx();
}