Arrays in VB Classic use a 0-based indice. UBound returns -1 if the array has no elements, 0 if it has 1, 1 if it has 2, etc.

In VB Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

• .BAS = VB source code file.
• .CLS = VB class file (one class per file).

By Reference or Value
For parameters, you can optionally specify ByVal or ByRef. ByRef is the default if you don't specify.

Short-circuit evaluation is a feature of most languages where once an evaluation evaluates to False, the compiler evaluates the whole expression to False, exits and moves on to the next code execution line. In VB Classic, the if statement does not support short-circuit evaluation but you can mimic it. Use either an if..else if..else if statement or nested if statements. You will find that your code that makes use of this technique will be clearer and easier to maintain than the short-circuit equivalent and faster than ingnoring the issue.

VB Classic uses = for it's assignment operator.

VB Classic is not case sensitive. If you type any other case for commands or variables, VB Classicwill change it to the "accepted" or "defined" case. For example, if you type msgbox it is converted to MsgBox.

VB Classiccode blocks are surrounded by statement ending keywords that all use End such as End Sub, End If, and WEnd.

Commenting Code
VB Classic, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). VB Classic does NOT have a multiple line comment.

Directives - #

Directives are sometimes called compiler or preprocessor directives. A # is used for directives within VB Classic code. VB Classic offers only an #If..then/#ElseIf/#Else directive.

Save as VB Classic. Common comparison operators:

Scope can be Public, Global, or Private. The use of the newer Public keyword is preferred to the older Global. Private Const is the same as just specifying Const.

VB applications require the VB runtime DLL (for version 6, it's VB600.DLL) plus any additional dependencies you've added such as Crystal Reports, ActiveX controls, and DLLs.

You can use any of the many free and commercially available installation packages.

Languages Focus: Development Tools

Primary development tool(s) used to develop and debug code.

Languages Focus: End of Statement

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

The End If is optional if you put your code on a single line.

Literals are quoted as in "Prestwood". If you need to embed a quote use two quotes in a row.

Language Overview: Class based language. Although you can create classes, VB Classic is not fully OOP. It is a traditional language with a few OOP extensions. You code in a traditional approach using functions, procedures, and global data, and you can make use of simple classes to help organize your reusable code. It also supports one-level abstract class to implemented class using the Implements keyword.

Target Platforms: Microsoft Visual Basic 6 is most suitable for creating Windows desktop applications that use the VB600.DLL runtime DLL within Microsoft Windows.

Crystal Reports was very popular with VB Classic developers and came bundled with Visual Basic 3 through 6. VB6 offers both Crystal Reports and the new Microsoft Data Report Designer.

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

An operation with only one operand (a single input) such as + and -.

VB Classic is a loosely typed language. Declaring variables is optional unless you use the Option Explicit statement to force explicit declaration of all variables with Dim, Private, Public, or ReDim. Using Option Explicit is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope.

Undeclared variables are variants. To specifically declare a variant, use:

Dim x As Variant

Dim x 

Common data types include Byte (0..255), Boolean, Integer (2-byte integers), Long (4-byte integers), Currency, Single (32-bit number), Double (64-bit number), Date, String, and variant.

Variables declared with Dim at the module level are available to all procedures within the module. At the procedure level, variables are available only within the procedure.

VB Classic logical operators:

In addition to Add and Item, collections also offer Count and Remove. Notice that Add uses the format of Value, Key (which is backwards from many other languages).

One class per file. File must use a .cls extension (instead of .bas). You can include your classes in your project (a traditional OOP approach) or compile them to a DLL or ActiveX EXE, register them, and use them that way (a uniquely VB approach).

VB Classic is a non-OOP language with some OOP features. It offers both Subs and Functions. A Sub does not return a value while a Function does. When Subs and Functions are used in a class module, they become the methods of the class.

Developer defined overloading in VB Classic:

• Operator - No
• Method - No

The Me keyword is a built-in variable that refers to the class where the code is executing. For example, you can pass Me from one module to another.

VB Classic Left of String

When an object instance is created from a class, VB6 calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, VB6 calls a special sub called Class_Terminate.

When an object instance is destroyed, VB6 calls a special parameter-less sub named Class_Terminate. For example, when the variable falls out of scope. Since you cannot specify parameters for this sub, you also cannot overload it.

When an object instance is created from a class, VB6 calls a special sub called Class_Initialize.

VB classic supports only a single "level" of interface inheritance (abstract class to implimentation class). See Implements in VB's help.

VB classic supports only a single "level" of inheritance (abstract class to implimentation class).

VB6 has limited support for interfaces. You can create an interface of abstract methods and properties and then implement them in one or more descendant classes. It's a single level implementation though (you cannot inherit beyond that). The parent interface class is a pure abstract class (all methods and properites are abstract, you cannot implement any of them in the parent class).

In the single level descendant class, you have to implement all methods and properties and you cannot add any. Your first line of code is Implements InterfaceName.

VB classic uses the keywords sub and function. A sub does not return a value and a function does. Many programmers like to use the optional call keyword when calling a sub to indicate the call is to a procedure.

In VB Classic, the keywords Private, Friend, Public, and Static are used to set access levels for declared elements.