Having trouble with transfering 2 different ProductID to the next page

i am currently embarking on a project regarding products catalog. I have check box above the image. So whenever, i checked 2 , i want to transfer 2 different Product Id and display 2 images in the next page. However, i am not able to do that. I can only transfer 1 selected image only . is there any way there once i checked 3 checkboxes, it will show me 3 items on the next page? Great help will be appreciated!!

void GetCheckedBox()
{
    foreach (DataListItem li in DataList1.Items)
    {
         selectedProducts = selectedProducts + "," + cb.Value; 
         LblText.Text = selectedProducts;

         Product.Add(selectedProducts);

         string url = "CompareProducts.aspx?prodId=" + selectedProducts.Substring(selectedProducts.LastIndexOf(',') + 1);

         Response.Redirect(url);
         //  DataList1.DataBind();

        }
    }
}

My ProductID is in string form : 0001,0002, 0003