Data Types and Operators in VB6.0

VISUAL BASIC 6.0 - VARIABLE, CONSTANT, DATA TYPES and OPERATORS

VARIABLE

A Variable is a named storage locations in memory.

The declared variables can easily be referenced in other places in the application code.

The value of the variable does not change during program execution of a VB application.

Variables can be declared in form, module or global scope and can be public or private.

Naming Rules

Each programmer has to name the variables

1.Name may consist of letters, digits and underscores

2.It must be 1 to 255 characters in length

3.It may not be reserved words (keywords)

General Form

[Scope] Dim Identifier [As Datatype] = value

Example

Dim StuName as String

Dim count as Integer

CONSTANT

Constants are named storage locations in memory.

The value of constant does not change during program execution.

Constants can be declared in form, module or global scope and can be public or private.

General Form

[Scope] Const Identifier [As Datatype] = value

Example

Const PI = 22/7

Public Const gravity As Single = 9.81

Private Const PI As Single = 3.14

Predefined Visual Basic Constants

The predefined constants can be used anywhere in the code and define / assign the default values.

Example

Consider a statement that will set the window state of a form to be maximized.

Form1.Windowstate = 2 (or)

Form1.WindowState = vbMaximized

DATA TYPES IN VB 6.0

The data type of a variable or constant indicates what type of information will be stored in the allocated memory space: perhaps a name, date, age or amount.

When a variable is declared, a data type is assigned for it that determines the kind of data they can store.

By default VB variables are of variant data types which allow storing numeric, date / time or string data.

The fundamental data types in VB include integer, long, single, double, string, currency, byte and boolean.

In addition, some types can interchange with some other types.

A list of VB's data types are given below with minimum and maximum values ​​it can hold

1. Numeric

Byte	Store integer values ​​in the range of 0 - 255
Integer	Store integer values ​​in the range of (-32,768) - (+ 32,767)
Long	Store integer values ​​in the range of (- 2,147,483,468) - (+ 2,147,483,468)
Single	Store floating point value in the range of (-3.4x10 -38 ) - (+ 3.4x10 38 )
Double	Store large floating value which exceeding the single data type value
Currency	Store monetary values. It supports 4 digits to the right of decimal point and 15 digits to the left

2. String

Use to store alphanumeric values. A variable length string can store approximately 4 billion characters

3. Date

Use to store date and time values. A variable declared as date type can store both date and time values ​​and it can store date values ​​like mm / dd / yyyy.

4. Boolean

Boolean data types hold either a true or false value. These are not stored as numeric values ​​and cannot be used as such. Values ​​are internally stored as 1 (True) and 0 (False) and any non-zero value is considered as true.

5. Variant

Stores any type of data and is the default VB data type. In VB if we declare a variable without any data type by default the data type is assigned as default.

Here is a list of the most common data types and their prefixes:

Data Type	Prefix	Example
Boolean	bln	blnFound
Byte	byt	bytTracks
Date / Time	dtm	dteStartOfShift
Double	dbl	dblDistance
Error	err	errCantOpen
Integer	int	intNbrOfStudents
Long	lng	lngPopulation
Object	obj	objConnection
Single	sng	sngAge
String	str	strCountryName
Currency	cur	curHourlySalary
Variant	var	varFullName

Example

Private Sub Form_Load()

    Dim CountryName As String

    Dim IsMarried As Boolean

    Dim StudentAge As Byte

    Dim Tracks As Integer

    Dim Population As Long

    Dim Distance As Single

    Dim StartingSalary As Currency

    Dim DateOfBirth As Date

    Dim KickOffTime As Date

End Sub

 

OPERATORS IN VB

An operator is a symbol that performs some mathematical or logical operations.

Generally in VB 6.0, there are three types of operators. 

Arithmetical Operators

To perform various arithmetic operations like addition, subtraction, multiplication, division and exponentiation

Operators	Description	Example	Result
+	Add	5+5	10
-	Subtract	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	"GOOD"&" "&"LUCK"	"GOOD LUCK"

Relational Operators

To form conditions, 6 relational operators are used to compare values.  The result of the comparison is either True or False.

Operators	Description	Example	Result
>	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

To create compound conditions (to test more than one condition) by using logical operators, which is always True or False.

Operators	Description
OR	Operation will be true if either of the operands is true
NOT	Operation will be true if not equal to the operands is true
AND	Operation will be true only if both the operands are true