How should I change the visibility of a TextBox when a ComboBox value changes?

I'm new to programming and I'm trying to change the value of a textbox depending of a selected value on a combo box, since the values are numerical 1 to 20, and depending on the selection it will be the number of text boxes visible. I'm using the event selected index changed.

Here is my code:

private void cbxPIN_SelectedIndexChanged(object sender, EventArgs e)
{
    int pines = Convert.ToInt32(cbxPIN.SelectedItem.ToString());
    if (pines == 1)
    {
        textbox1.visible = true;
    }
    else if (pines == 2)
    {
        textbox1.visible = true;
        textbox2.visible = true;
    }
 ...

    else if (pines == n)
    {
        textbox1.visible = true;
        textbox2.visible = true;
 ...
        textboxn.visible = true;
    }
}

since there are like 25 different numeric values on the combo box is there an easier way of doing this? asides from comparing each different value?

Something like a loop.