Adding Particular columns value in gridview

       double sum = 0;
        for (int x = 0; x < GridView1.Rows.Count; x++)
        {
            sum += Convert.ToDouble(GridView1.Rows[x].Cells[3].Text);
        
        }
 

Txt_amo.Text = sum.ToString();

Here cell[3] indicate the cell value which i am going to sum

Txt_amo.Text = sum.ToString();