How to generate dynamic TextBoxes based on count selected in DropDownList in ASP.Net

You can use Repeater for this.

HTML

<div>
    Numbers of TextBox
    <asp:DropDownList ID="ddlNumberOfRows" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlNumberOfRows_SelectedIndexChanged">
        <asp:ListItem Text="One" Value="1" />
        <asp:ListItem Text="Two" Value="2" />
        <asp:ListItem Text="Three" Value="3" />
    </asp:DropDownList>
    <br />
    <br />
    <asp:Repeater ID="Repeater1" runat="server">
        <ItemTemplate>
            <%#Container.ItemIndex+1 %>
            <asp:TextBox ID="txtTextBox1" runat="server" />
        </ItemTemplate>
        <SeparatorTemplate>
            <br />
        </SeparatorTemplate>
    </asp:Repeater>
</div>

 C#

protected void ddlNumberOfRows_SelectedIndexChanged(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("TextBox");
    int count = Convert.ToInt32(ddlNumberOfRows.SelectedItem.Value);
    for (int i = 0; i < count; i++)
    {
        dt.Rows.Add("");
    }
    this.Repeater1.DataSource = dt;
    this.Repeater1.DataBind();
}

Screenshot