How to do Total sum in Gridview Footer in Asp.net C# ?

decimal a = 0;
            Int32 y = GridView1.Items.Count;
            for (Int32 i = 0; i < y ; i++)
            {

                a = a + Convert.ToDecimal(((Label)GridView1.Items[i].FindControl("lbl_subtoprice")).Text.ToString());

            }

            lbl_grandtotal.Text = Convert.ToString(a);

lbl_subtopricel id of your durations values
and
lbl_grandtotal is id of label in footer

var result = from p in st.prices select new {
            p.id,
              p.Name,
               p.price1 };
            GridView1.DataSource = result;
            GridView1.DataBind();
            double sum=0;
            foreach(var item in result){

                sum += Convert.ToDouble(item.price1);
            }
            Label lblsum = (Label)GridView1.FooterRow.FindControl("Lbltotal");
            lblsum.Text = sum.ToString();