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Introduction
 | Visual Basic 6 (VB6) is a Microsoft product with a lineage since 1991. |
| VB6 is an object-based programming environment. While it has a number of object oriented features, it is not a "complete" object oriented development environment. |
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| VB6 is one of the most popular Windows software development tools. |
| VB6 is built around an integrated development environment (IDE) that allows rapid development of user interfaces and the supporting code. |
| VB has spawned a number of variants including VBScript for web applications (browser and server). |
| VB.Net has been released as a "replacement" for VB6 although Microsoft has promised VB6 product support until 2008. |
Language Fundamentals
Program Structure and Organization
| VB6 programs are organized by global declarations, functions, and subroutines. | ||||||||||
| Source files are ASCII text, but must be edited via the IDE. The source file contains code to define graphic and program objects developed in the IDE (e.g., buttons, text boxes, etc.). | ||||||||||
| Program structure
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| Language/character sets: execution character sets can vary based on Windows environment; development environment is ASCII text. | ||||||||||
| Identifiers and keywords: VB6 has a number of key words and identifiers. | ||||||||||
| VB6 programs are organized into projects (defined as a project files; .prj); supporting files define windows (form files; .frm), global files (.bas), and a number of other supporting files for class/object declarations and so forth. | ||||||||||
| VB6 programs are compiled to machine language. They depend on a set
of supporting DLLs to run even the most basic of applications. VB6 can
also be used to create the following:
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Data Types
Data Type |
Storage Size |
Range |
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Byte |
1 byte |
0 to 255 |
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Boolean |
2 bytes |
True or false |
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Integer
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2 bytes |
-32,768 to 32,767 |
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Long
(long integer) |
4 bytes |
-2,147,483,648 to 2,147,483,647 |
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Single
(single-precision floating-point) |
4 bytes |
-3.402823E38 to -1.401298E-45 for negative
values;
1.401298E-45 to 3.402823E38 for positive
values |
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Double
(double-precision floating-point) |
8 bytes |
-1.79769313486232E308 to -4.94065645841247E-324 for negative values;
4.94065645841247E-324 to |
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Currency (scaled integer) |
8 bytes |
-922,337,203,685,477.5808 to
922,337,203,685,477.5807 |
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Decimal |
14 bytes |
+/-79,228,162,514,264,337,593,543,950,335
with no decimal point;
+/-7.9228162514264337593543950335 with 28
places to the right of the decimal;
smallest non-zero number is +/-0.0000000000000000000000000001 |
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Date |
8 bytes |
January 1, 100 to December 31, 9999 |
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Object |
4 bytes |
Any Object reference |
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String or text data… |
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String (variable-length) |
10 bytes + string length |
0 to approximately 2 billion
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String (fixed-length) |
Length of string |
1 to approximately 65,400 |
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Variant (with numbers) |
16 bytes |
Any numeric value up to the range of a Double |
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Variant (with characters) |
22 bytes + string length |
Same range as for variable-length String |
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User-defined (using Type) |
Number required by elements |
The range of each element is the same as the
range of its data type. |
| Variables are declared via the "dim" statement. Application level or global variables are defined by the "global" keyword. | ||||||
| VB6 will allow you to create programs in which variables do not have to be declared. These variables are dynamically scoped during compilation as Variant data types. | ||||||
| Variable scope:
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| Arrays: VB6 supports multi-dimensional arrays of all data types. Arrays can be extended at runtime and data preserved. |
Expressions and Operators
Arithmetic
Operators used to perform mathematical calculations.
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^ —Exponent Operator |
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* —Multiply Operator |
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/ —Division Operator |
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\ —Division, Return Integer Operator |
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Mod —Modulo Operator |
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+ —Add Operator |
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- —Subtract Operator |
Comparison operators
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= —Equal |
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<> —Not Equal |
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< —Less Than |
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> —Greater Than |
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<= —LessThan or Equal |
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>= —Greater Than or Equal |
Concatenation operators used to combine strings.
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+, & for combining strings |
Logical Operators
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And Operator |
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Not Operator |
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Or Operator |
Control Statements
| If-then
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| Select
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| Do/While loop
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| For loop
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| Go To: jump to a labeled destination; within a subroutine or function only. | ||||||
| Exit: break out of a loop, subroutine, or function. |
Input/Output
VB6 is a windows-based development environment.
The VB6 input/output is determined via window forms that include a variety of built-in or intrinsic objects including:
| Form including the ability to add menus (with submenus) |
| Text input box |
| Radio buttons |
| Check boxes |
| List and drop down lists |
| Command button |
| Horizontal and scrolling bars |
| Picture and image controls (hold and display graphics) |
| File objects (drives, directories, and files) |
| Frames containers to hold other objects |
| Basic database object |
In addition to the above objects, the VB6 professional set of controls and third-party ActiveX controls enable developers to add a number of capabilities including:
| Grid structures |
| Rich text controls |
| Special purpose controls, API interfaces |
| Database controls |
VB6 also includes:
| File I/O: basic functions to open and close files; input, output, and append to files. There are a number of functions to read and write single characters/bytes, lines, records, and entire files. |
| Database: interface to database interface libraries such as ActiveX Data Objects (ADO). |
Libraries and Support
VB6 includes a rich built-library of support routines and functions including:
| String handling |
| Date and time |
| Formatting |
| Math functions |
| Financial |
The following table summarizes many of the built-in functions provided by VB6:
| Category | Keywords |
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| Array handling | Array Dim, Private, Public, ReDim IsArray Erase LBound, UBound |
| Assignments | Set |
| Conversions | Abs Asc, AscB, AscW Chr, ChrB, ChrW CBool, CByte CCur, CDate CDbl, CInt CLng, CSng, CStr DateSerial, DateValue Hex, Oct Fix, Int Sgn TimeSerial, TimeValue |
| Dates/Times | Date, Time DateAdd, DateDiff, DatePart DateSerial, DateValue Day, Month, MonthName Weekday, WeekdayName, Year Hour, Minute, Second Now TimeSerial, TimeValue |
| Formatting Strings | Format FormatCurrency FormatDateTime FormatNumber FormatPercent |
| Input/Output | InputBox LoadPicture MsgBox |
| Literals | Empty False Nothing Null True |
| Math | Atn, Cos, Sin, Tan Exp, Log, Sqr Randomize, Rnd |
| Miscellaneous | Eval Function Execute Statement RGB Function |
| Strings | Asc, AscB, AscW Chr, ChrB, ChrW Filter, InStr, InStrB InStrRev Join Len, LenB LCase, UCase Left, LeftB Mid, MidB Right, RightB Replace Space Split StrComp String StrReverse LTrim, RTrim, Trim |
| Variants | IsArray IsDate IsEmpty IsNull IsNumeric IsObject TypeName VarType |
Resources
References
| Microsoft VB6 Reference: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon98/html/vbstartpage.asp |
| Google Directory: http://directory.google.com/Top/Computers/Programming/Languages/Visual_Basic/ |
Tutorials
| http://spazioinwind.libero.it/vbprogzone/tutorials/learnvb1.html |