Validate ASP.Net TextBox for specific length of digit (number) and alphabets using C# and VB.Net

Hi akhter,

Refer below example.

HTML

<asp:TextBox runat="server" ID="txtUser" />
<asp:Button Text="Validate" runat="server" OnClick="OnValidate" />
<br />
<asp:Label ID="lblMessage" runat="server" ForeColor="Red" />

Code

C#

protected void OnValidate(object sender, EventArgs e)
{
    lblMessage.Text = "";
    string userName = txtUser.Text.Trim();
    string number = new String(userName.Where(Char.IsDigit).ToArray());
    string alphabel = new String(userName.Where(Char.IsLetter).ToArray());

    if (number.Length > 4 || alphabel.Length > 4)
    {
        lblMessage.Text = "Four alphabet and four Digits allowed.";
    }
}

VB.Net

Protected Sub OnValidate(ByVal sender As Object, ByVal e As EventArgs)
    lblMessage.Text = ""
    Dim userName As String = txtUser.Text.Trim()
    Dim number As String = New String(userName.Where(Function(x As Char) Char.IsDigit(x)).ToArray)
    Dim alphabel As String = New String(userName.Where(Function(x As Char) Char.IsLetter(x)).ToArray)

    If number.Length > 4 OrElse alphabel.Length > 4 Then
        lblMessage.Text = "Four alphabet and four Digits allowed."
    End If
End Sub

Screenshot