Hi yohana,
I have created sample code which fullfill requirement.
HTML
<div>
<asp:TextBox ID="txtNumber" runat="server" />
<asp:Button Text="Submit" OnClick="Submit" runat="server" />
<br />
<asp:Label ID="lblnumbers" Text="" runat="server" />
</div>
C#
protected void Submit(object sender, EventArgs e)
{
lblnumbers.Text = "";
string mytext = txtNumber.Text;
char[] myChars = mytext.ToCharArray();
foreach (char ch in myChars)
{
if (char.IsDigit(ch))
{
lblnumbers.Text += ch.ToString();
}
}
}
Screenshot
![](https://i.imgur.com/IDhYdPp.gif)
I hope works for you.