Visual Basic uses building blocks such as Variables, Data Types, Procedures, Functions and Control Structures in its programming environment. This section concentrates on the programming fundamentals of Visual Basic with the blocks specified.
Modules
Code in Visual Basic is stored in the form of modules. The three kind of modules are Form Modules, Standard Modules and Class Modules. A simple application may contain a single Form, and the code resides in that Form module itself. As the application grows, additional Forms are added and there may be a common code to be executed in several Forms. To avoid the duplication of code, a separate module containing a procedure is created that implements the common code. This is a standard Module.
Class module (.CLS filename extension) are the foundation of the object oriented programming in Visual Basic. New objects can be created by writing code in class modules. Each module can contain:
Declarations : May include constant, type, variable and DLL procedure declarations.
Procedures : A sub function, or property procedure that contain pieces of code that can be executed as a unit.
These are the rules to follow when naming elements in VB - variables, constants, controls, procedures, and so on:
- A name must begin with a letter.
- May be as much as 255 characters long (but don't forget that somebody has to type the stuff!).
- Must not contain a space or an embedded period or type-declaration characters used to specify a data type; these are ! # % $ & @
- Must not be a reserved word (that is part of the code, like Option, for example)
- The dash, although legal, should be avoided because it may be confused with the minus sign. Instead of First-name use First_name or FirstName.
Data types in Visual Basic 6
By default Visual Basic variables are of variant data types. The variant data type can store numeric, date/time or string data. When a variable is declared, a data type is supplied for it that determines the kind of data they can store. The fundamental data types in Visual Basic including variant are integer, long, single, double, string, currency, byte and boolean. Visual Basic supports a vast array of data types. Each data type has limits to the kind of information and the minimum and maximum values it can hold. In addition, some types can interchange with some other types. A list of Visual Basic's simple data types are given below.
Data type Storage size Range
Byte 1 byte 0 to 255
Boolean 2 bytes True or False
Integer 2 bytes -32,768 to 32,767
Long (long integer) 4 bytes -2,147,483,648 to 2,147,483,647
Single 4 bytes (-3.4x10-38) - (+ 3.4x1038)
Double 8 bytes -1.79769313486232E308 to -4.94065645841247E-324
Currency (scaled integer) 8 bytes -922,337,203,685,477.5808 to 922,337,203,685,477.5807
Date 8 bytes January 1, 100 to December 31, 9999
Object 4 bytes Any Object reference
String (variable-length) 10 bytes + string length 0 to approximately 2 billion
String (fixed-length) Length of string 1 to approximately 65,400
Variant (with numbers) 16 bytes Any numeric value up to the range of a Double
Variant (with characters) 22 bytes + string length Same range as for variable-length String
User-defined (using Type) Number The range of each element is the same as the range of its
data type.
Byte 1 byte 0 to 255
Boolean 2 bytes True or False
Integer 2 bytes -32,768 to 32,767
Long (long integer) 4 bytes -2,147,483,648 to 2,147,483,647
Single 4 bytes (-3.4x10-38) - (+ 3.4x1038)
Double 8 bytes -1.79769313486232E308 to -4.94065645841247E-324
Currency (scaled integer) 8 bytes -922,337,203,685,477.5808 to 922,337,203,685,477.5807
Date 8 bytes January 1, 100 to December 31, 9999
Object 4 bytes Any Object reference
String (variable-length) 10 bytes + string length 0 to approximately 2 billion
String (fixed-length) Length of string 1 to approximately 65,400
Variant (with numbers) 16 bytes Any numeric value up to the range of a Double
Variant (with characters) 22 bytes + string length Same range as for variable-length String
User-defined (using Type) Number The range of each element is the same as the range of its
data type.
In all probability, in 90% of your applications you will use at most six types: String, Integer, Long, Single, Boolean and Date. The Variant type is often used automatically when type is not important. A Variant-type field can contain text or numbers, depending on the data that is actually entered. It is flexible but it is not very efficient in terms of storage.
Operators in Visual Basic
Arithmetical Operators
+ Add 5+5 10
- Substract 10-5 5
/ Divide 25/5 5
\ Integer Division 20\3 6
* Multiply 5*4 20
^ Exponent (power of) 3^3 27
Mod Remainder of division 20 Mod 6 2
& String concatenation "George"& " "&"Bush" "George Bush"
Relational Operators
> Greater than 10 > 8 True
< Less than 10 < 8 False
>= Greater than or equal to 20>=10 True
<= Less than or equal to 10<=20 True
<> Not Equal to 5<>4 True
= Equal to 5=7 False
Logical Operators
OR Operation will be true if either of the operands is true
AND Operation will be true only if both the operands are true
