How to Update the Rows Selected in the Grid View In the SQL Server

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C#

SQL-Server

Hi,
I am New to C#, In my Project I have a Page that displays the Registered Systems for Approval in the Grid View I have a Check box Template Field in the Grid View for Selection and Button outside the Gridview for the selected row to be Updated I had tried with the Following code for Updation but it excecutes only the Else part that "Select atleast one Row" even if I select a Check Box My Code is,

protected void Button1_Click(object sender, EventArgs e)
       {

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

               CheckBox cb = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("chkSelect");

               if (cb != null && cb.Checked)
               {
                   using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["EvalCon"].ConnectionString))
                   {
                       string sqlqry = "Update Sysinfo Set Appflag='W',PApprovedate=getdate() where Mac_id=' " + GridView1.Rows[i].Cells[0].ToString()+ "'";
                       try
                       {
                           using (SqlCommand cmd = new SqlCommand(sqlqry, conn))
                           {
                               cmd.CommandType = CommandType.StoredProcedure;
                               conn.Open();
                               cmd.ExecuteNonQuery();
                               lblMessage.Visible = true;
                               lblMessage.Text = "Selected System(s) has been Approved Successfully...";
                           }
                       }
                       catch (SqlException ex)
                       {
                           if (ex.Message.Contains("SQL"))
                           {
                               lblMessage.Visible = true;
                               lblMessage.ForeColor = System.Drawing.Color.Red;
                               lblMessage.Text = "Error Occured Continue Kindly Contact Administartor!!!";
                           }
                       }
                       finally
                       {
                           conn.Close();
                           conn.Dispose();
                       }
                   }
               }
               else
               {
                   lblMessage.Visible = true;
                   lblMessage.ForeColor = System.Drawing.Color.Red;
                   lblMessage.Text = "Select Atleast One Row!!!";

               }

           }

       }

Can Anybody help me out with Example Coding....