这是我刚做的关于复选框选择次数显示在LABLE里，可是再选别的选项，前个选项就被覆盖了、求解答

if (CheckBoxList1.SelectedIndex == 0)
         {
             L1 .Text  = "1";
            
         }
         else
         {
             L1.Text  = "0";
            
         }
         if (CheckBoxList1.SelectedIndex == 1)
         {
             L2.Text = "1";

         }
         else
         {
             L2.Text = "0";

         }
         if (CheckBoxList1.SelectedIndex == 2)
         {
             L3.Text = "1";

         }
         else
         {
             L3.Text = "0";

         }
         if (CheckBoxList1.SelectedIndex == 3)
         {
             L5.Text = "1";

         }
         else
         {
             L5.Text = "0";

         }