multiple checked items value insert in single column c#

Question

how to insert multiple checked value in single column in c# 

 like i select value like this:

 

 

<asp:DropDownCheckBoxes ID="ddsize" runat="server" UseButtons="true" >

 

<asp:ListItem Text="Queen" Value="1"></asp:ListItem>

<asp:ListItem Text="Twin" Value="2"></asp:ListItem>

<asp:ListItem Text="Round" Value="3"></asp:ListItem>

<asp:ListItem Text="King" Value="4"></asp:ListItem> 

</asp:DropDownCheckBoxes>

 

 

int str =0;

for (int i = 0; i <= ddsize.Items.Count - 1; i++)

{

if (ddsize.Items[i].Selected)

{

if (str ==0)

{

str =int.Parse( ddsize.Items[i].Value);

}

else

{

str +=int.Parse(ddsize.Items[i].Value);

}

}

}

 

 

select value 1 and 2 and 3 then

 

i want insert all id in single column