Build Your Own Application with 4GL and the VDC

Welcome. This guide teaches you how to write your own business applications using the Aubit 4GL language together with the VDC desktop client (currently VDC5, a modern Qt-based GUI).

You do not need any prior 4GL experience. We start from a single line of code, build up to real forms and database access, and finish with the commands you use to compile and ship a complete program.

What is this stack?

You write your program once, in a compact business-oriented language, and it runs behind a rich graphical client — without writing a single line of GUI code by hand.

Layer	What it is	Your job
Aubit 4GL	A 4th-generation language for data-driven business apps	Write the logic and the screens
Form (.per)	A plain-text description of a screen and its fields	Lay out fields, pick widgets
VDC client	The graphical front-end the user actually sees and clicks	Nothing — it renders your forms

The client / server model

The key idea: your program and the screen run in two different places.

   +------------------------+            XML protocol             +---------------------+
   |  Your 4GL program      |  <------------------------------>   |  VDC client (GUI)   |
   |  (logic + SQL + forms) |        over a TCP connection        |  windows, buttons,  |
   |  runs on the server    |                                     |  fields, the mouse  |
   +------------------------+                                     +---------------------+

Your compiled program contains the business logic and the database access. It does not draw anything itself. Instead it sends a description of each window to the VDC client, and the client draws it, collects what the user types, and sends the results back. This is why the same program works on a desktop client and a mobile client without any code change.

You will set up this connection in Getting Started.

How this guide is organized

Read it in order the first time — each chapter builds on the previous one. Later, use it as a reference.

#	Chapter	You will learn
1	Getting Started	Set up the tools, connect to the client, run your first program
2	Language Basics	Variables, control flow, functions, arrays, the gotchas
3	Forms and Widgets	Write a .per form; every field type and its attributes
4	Screens, Input and Menus	Display data, collect input, drive a window with a menu
5	Working with Arrays	Show and edit lists with DISPLAY ARRAY / INPUT ARRAY
6	Talking to the Database	SELECT, cursors, INSERT/UPDATE/DELETE, transactions
7	Talking to the VDC Client	Themes, hiding fields, toast notifications, modern features
8	Building and Running	Compile single files, multi-file programs, forms, libraries
9	Quick Reference	Data types, operators, built-in functions, environment vars
10	UI Function Reference	Every ui.* call: titles, fields, combos, toasts, progress, documents
11	Language Reference	Every statement and built-in function, with syntax
12	Command-line Tools	4glc, 4glpc, fcompile, database & analysis tools

What you will build

By the end you will be able to write a small but complete application: a window with a form, fields the user can edit, a scrollable list of records, full database read/write, and the commands to compile and run it.

A note on style. The examples here are deliberately neutral and self-contained. Type them in, compile them, run them, and change them. That is the fastest way to learn 4GL.

Ready? Start with Getting Started.