Finding CheckBoxes in gridview

Follow these steps to find the checkboxes in gridview 

StringBuilder str = new StringBuilder();

        for (int i = 0; i < GridView1.Rows.Count; i++)

        {

            bool ischecked = ((CheckBox)GridView1.Rows[i].FindControl("Chk1")).Checked;

            if (ischecked)

            {

                str.Append(GridView1.Rows[i].Cells[1].Text);

            }

        }

        Response.Write(str.ToString());