Limiting entry to numeric characters for a textbox

1) Declare a variable to hold JavaScript for enabling only Numbers as follows:

Dim strNumberOnlyValidation As String = "if (event.keyCode < 48 || event.keyCode > 57) event.returnValue = false;"

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2) Link the above JavaScript Variable to the requested TextBox as follows in Page_Load:

MyTextBox.Attributes("onKeypress") = strNumberOnlyValidation

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You may find a list of JavaScript KeyCodes here:

Like this

<asp:TextBox runat="server" id="txtNumber" />
<asp:RegularExpressionValidator runat="server" id="rexNumber" controltovalidate="txtNumber" validationexpression="^[0-9]+$" errormessage="Please enter digit only!" />

OR

<asp:TextBox runat="server" id="txtNumber" />
<asp:RegularExpressionValidator runat="server" id="rexNumber" controltovalidate="txtNumber" validationexpression="\d+" errormessage="Please enter digit only!" />

Try This:
<asp:RegularExpressionValidator runat="server" id="rexNumber"
            controltovalidate="txtSN1" validationexpression="(^-?\d\d*\.\d*$)|(^-?\d\d*$)|(^-?\.\d\d*$)" errormessage="Please enter digit only!" />

http://regexlib.com/DisplayPatterns.aspx?cattabindex=2&categoryId=3

Sorry, it is a windows application, not an asp.net application
thank you