checkedListBox

 private void button3_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < checkedListBox1.Items.Count; i++)
            {
                if (checkedListBox1.GetItemChecked(i))
                {
                    checkedListBox1.Items.RemoveAt(i);
                    i--;
                }
            }

 private void button11_Click(object sender, EventArgs e)
        {
                for (int i = 0; i < checkedListBox1.Items.Count; i++)
                {
                    if (checkedListBox1.GetItemChecked(i))
                    {
                        checkedListBox1.SetItemChecked(i, false);
                    }
                    else
                    {
                        checkedListBox1.SetItemChecked(i, true);
                    }
                }
            }