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ASP Variables and Types

Understand the values a VBScript Variant can hold.

How it works

VBScript variables contain Variants. A Variant may hold a string, number, date, Boolean, Empty, Null or an object reference. Those cases behave differently. Use Set for object references and inspect values with IsEmpty or IsNull rather than guessing from how a response looks. Keep integer quantities separate from display labels.

Use the separate Windows lab

This is a legacy-maintenance course. Classic ASP uses IIS and VBScript; ASP.NET Web Pages uses .NET Framework and Razor. Neither runs in PHP, Apache or Bhylu’s browser playground. The reviewed baseline is 32-bit IIS Express 10.0.2001, .NET Framework 4.8, Web Pages / Razor 3.2.9 and the Windows VBScript engine. ADO database examples use the actual 32-bit Jet OLE DB 4.0 provider, not SQL Server or XAMPP MySQL.

Download download-lab.mjs into a separate empty learning folder. Run node download-lab.mjs to fetch hash-checked source files into a new bhylu-asp-lab folder, then cd bhylu-asp-lab and node run-lab.mjs --start. Before deployment, local preview uses node download-lab.mjs http://127.0.0.1:8000/examples/asp/. The source downloader refuses an existing destination. Review its source before running it.

The foreground launcher needs your own 32-bit IIS Express installation with Classic ASP, .NET Framework 4.8 and the VBScript engine available. It downloads the three pinned Web Pages packages from NuGet into its private cache, binds only localhost on port 8142 and stops when you press Ctrl+C. Keep its console open. Visit http://localhost:8142/variables-types.asp. It does not install IIS, enable Windows features, change Apache/PHP/MySQL, or publish any files. See the bundled README.txt for manual setup and test boundaries.

Each complete Classic ASP source requires the supplied Global.asa acknowledgement; Web Pages uses _PageStart.cshtml. Database and file examples create owned temporary files only under this private lab’s blocked App_Data folder. Sources are public text downloads; do not upload them as executable teaching endpoints on Bhylu.

Download variables-types.asp

Example

variables-types.asp

<%@ Language="VBScript" CodePage="65001" %>
<% Option Explicit
Response.Buffer = True
Response.ContentType = "text/plain"
Response.Charset = "utf-8"
If Application("BhyluLab") <> "YES" Then
    Response.Status = "403 Forbidden"
    Response.Write "Use the separate Bhylu learning lab."
    Response.End
End If
Dim unused, missing, seats
missing = Null
seats = 3
Response.Write IsEmpty(unused) & vbLf
Response.Write IsNull(missing) & vbLf
Response.Write TypeName(seats)
%>
Focus on the lesson operations

This excerpt omits shared lab setup. Use the complete download and supporting files to run it.

Lesson excerpt

Dim unused, missing, seats
missing = Null
seats = 3
Response.Write IsEmpty(unused) & vbLf
Response.Write IsNull(missing) & vbLf
Response.Write TypeName(seats)

Expected result

True
True
Integer

An undeclared-looking blank is not necessarily an empty string. unused is declared but uninitialised, while missing explicitly carries Null. TypeName describes the current value; later assignments can change that subtype.

Primary references

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