Creating a Grid Programmatically

 <div>
    <asp:Label ID="lblRowReq" Text="Required rows:" runat="server"></asp:Label>
    <asp:TextBox ID="txtRowReq" runat="server"></asp:TextBox>
     <asp:Button ID="btnRowGenrate" runat="server" Text="Generate Row" 
            onclick="btnRowGenrate_Click" />
    </div>
    <div>
    <asp:gridview ID="gvGenrateRow" runat="server" AutoGenerateColumns="false">
        <Columns>
        <asp:TemplateField HeaderText="Normal Text1">
            <ItemTemplate>
                <asp:TextBox ID="TextBox0" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Normal Text2">
            <ItemTemplate>
                <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Normal Text3">
            <ItemTemplate>
                <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Multiline Text">
            <ItemTemplate>
                 <asp:TextBox ID="TextBox3" runat="server" TextMode="MultiLine"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField> 
        <asp:TemplateField HeaderText="DropdownList">
            <ItemTemplate>
               <asp:DropDownList ID="ddlCategory" runat="server">
               <asp:ListItem Text="A"></asp:ListItem>
               <asp:ListItem Text="D"></asp:ListItem>
               <asp:ListItem Text="B"></asp:ListItem>
               </asp:DropDownList>
               
            </ItemTemplate>
        </asp:TemplateField>
        </Columns>
</asp:gridview>
    </div>

private void SetFirstRow()
      {

          DataTable dt = new DataTable();
          DataRow dr = null;
          dt.Columns.Add(new DataColumn("Column0", typeof(string)));
          dt.Columns.Add(new DataColumn("Column1", typeof(string)));
          dt.Columns.Add(new DataColumn("Column2", typeof(string)));
          dt.Columns.Add(new DataColumn("Column3", typeof(string)));
          dt.Columns.Add(new DataColumn("Column4", typeof(string)));

          dr = dt.NewRow();
          dr["Column0"] = string.Empty;
          dr["Column1"] = string.Empty;
          dr["Column2"] = string.Empty;
          dr["Column3"] = string.Empty;
          dr["Column4"] = string.Empty;

          dt.Rows.Add(dr);

          //Store the DataTable in ViewState
          ViewState["CurrentTable"] = dt;

          gvGenrateRow.DataSource = dt;
          gvGenrateRow.DataBind();
      }

      protected void btnRowGenrate_Click(object sender, EventArgs e)
      {
              SetFirstRow();
              for (int i = 0; i < Convert.ToInt32(txtRowReq.Text)-1; i++)
                  AddNewRowToGrid();
      }

      private void AddNewRowToGrid()
      {

          int rowIndex = 0;
          if (ViewState["CurrentTable"] != null)
          {
              DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
              DataRow drCurrentRow = null;
              if (dtCurrentTable.Rows.Count > 0)
              {
                  for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                  {
                      TextBox box0 = (TextBox)gvGenrateRow.Rows[rowIndex].Cells[0].FindControl("TextBox0");
                      TextBox box1 = (TextBox)gvGenrateRow.Rows[rowIndex].Cells[1].FindControl("TextBox1");
                      TextBox box2 = (TextBox)gvGenrateRow.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                      TextBox box3 = (TextBox)gvGenrateRow.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                      DropDownList ddl4 = (DropDownList)gvGenrateRow.Rows[rowIndex].Cells[4].FindControl("ddlCategory");

                      drCurrentRow = dtCurrentTable.NewRow();
                      drCurrentRow["Column0"] = box0.Text;
                      drCurrentRow["Column1"] = box1.Text;
                      drCurrentRow["Column2"] = box2.Text;
                      drCurrentRow["Column3"] = box3.Text;
                      drCurrentRow["Column4"] = ddl4.Text;
                      rowIndex++;
                  }

                  dtCurrentTable.Rows.Add(drCurrentRow);
                  gvGenrateRow.DataSource = dtCurrentTable;
                  gvGenrateRow.DataBind();
              }
          }
      }