1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Web;
 5 using System.Web.UI;
 6 using System.Web.UI.WebControls;
 7 using System.Data;
 8 using System.Data.SqlClient;
 9 using System.Configuration;
10 
11 public partial class _Default : System.Web.UI.Page
12 {
13     string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
14     protected void Page_Load(object sender, EventArgs e)
15     {
16         SqlConnection conn = new SqlConnection(constr);
17         conn.Open();
18         string sql = "select * from student";
19         SqlDataAdapter da = new SqlDataAdapter(sql, conn);
20         DataSet ds = new DataSet();
21         da.Fill(ds);
22         GridView1.DataSource = ds;
23         GridView1.DataBind();
24     }
25     protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
26     {
27         for (int i = 0; i <= GridView1.Rows.Count - 1; i++)
28         {
29             CheckBox chk = (CheckBox)GridView1.Rows[i].FindControl("chkCheck");
30             if (chkAll.Checked == true)
31             {
32                 chk.Checked = true;
33             }
34             else
35             {
36                 chk.Checked = false;
37             }
38         }
39     }
40 }

<asp:TemplateField>

                    <ItemTemplate>
                        <asp:CheckBox ID="chkCheck" runat="server" />
                    </ItemTemplate>
</asp:TemplateField>

<configuration>
  <connectionStrings >
    <add name="constr" connectionString="server=.\sqlexpress;database=db2016;uid=sa;pwd=123;"/>
  </connectionStrings>
    <system.web>
      <compilation debug="true" targetFramework="4.0" />
    </system.web>

</configuration>