public partial class _Default : System.Web.UI.Page
{
    DataSet ds = new DataSet();
    DataTable dt;
    DataColumn dc;
    protected void Page_Load(object sender, EventArgs e)
    {
        dt = ds.Tables.Add("Candidate");
        dc=dt.Columns.Add("CandidateID",typeof(Int32));
        dc = dt.Columns.Add("CandidateName", typeof(String));
        DataRow dr = ds.Tables["Candidate"].NewRow();
        dr["CandidateID"] =  1 ;
        dr["CandidateName"] = "Петя";
        ds.Tables["Candidate"].Rows.Add(dr);
        dr = ds.Tables["Candidate"].NewRow();
        dr["CandidateID"] =  2 ;
        dr["CandidateName"] = "Вася";
        ds.Tables["Candidate"].Rows.Add(dr);
        GridView1.DataSource = ds;
        GridView1.DataBind();
        GridView1.HeaderRow.Cells[ 0 ].Text = "Номер кандидата";
        GridView1.HeaderRow.Cells[ 1 ].Text = "Имя кандидата";
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        DataRow dr = ds.Tables["Candidate"].NewRow();
        dr["CandidateName"] = TextBox1.Text;
        dr["CandidateID"]=Convert.ToInt32(TextBox2.Text);
        ds.Tables["Candidate"].Rows.Add(dr);
        GridView1.DataBind();
     }
}