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ABOUT VB6.0



Introduction
Þ Visual Basic is a tool that allows you to develop Windows (Graphic User Interface – GUI) applications. The applications have a familiar appearance to the user.
Þ Visual Basic is event-driven; event driven meaning code remains idle until called upon to respond to some event (button pressing, menu selection). Visual Basic is governed by an event processor.
Þ The original Visual Basic for DOS and Visual Basic for Windows were introduced in 1991.


Steps in Developing Application
There are three primary steps involved in building a Visual Basic application:
1. Draw the user interface
2. Assign properties to controls
3. Attach code to controls

Rule for Variable
Variables are used by Visual Basic to hold information.
Þ No more than 40 characters
Þ They may include letters, numbers, and underscore (_)
Þ The first character must be a letter
Þ You cannot use a reserved word (word needed by Visual Basic)




Visual Basic Data Types
Data Type                               Suffix
Boolean                                   None
Integer                                    %
Long (Integer)                                     &
Single (Floating)                      !
Double (Floating)                    #
Currency                                 @
Date                                        None
String                                       $
Variant                                                None

Variable Declaration
There are three ways for a variable to be typed (declared):
1. Default
2. Implicit
3. Explicit
1. Default variable in visual basic is variant, by default the variant data type is a special type used by Visual Basic that can contain numeric, string, or date data.
2. Implicit type a variable, use the corresponding suffix shown above in the data type table.
For example,
TextValue$ = "This is a string" creates a string variable, while
Amount% = 300 creates an integer variable.
3. Explicit type a variable determines its scope. There are four levels of scope:
a. Procedure level
b. Global level
Within a procedure & for Global, variables are declared using the Dim statement:
Dim x as Integer
Dim y as Double
Dim name as String



Visual Basic Operators
1.      arithmetic operator with  order of precedence are:
Operator                    Operation
^                                  Exponentiation
*          /                      Multiplication and Division
Mod                             Modulus
+          -                      Addition and subtraction
2.      Comparison operators in Visual Basic:
Operator                    Comparison
>                                  Greater than
<                                  Less than
>=                                Greater than or equal to
<=                                Less than or equal to
=                                  Equal to
<>                                Not equal to

       3.  Logical operators
Operator                    Operation
Not                              Logical not
And                              Logical and
Or                                Logical or

Message box
The Message box displays a message, optional icon, and selected set of command buttons.
The statement form of the message box returns no value (it simply displays the box):
MsgBox Message, Type, Title
where
Message Text message to be displayed
Type Type of message box (discussed in a bit)
Title Text in title bar of message box
Value                                     Meaning                                 Symbolic Constant
1                                              OK button selected                            vbOK
2                                              Cancel button selected                       vbCancel
3                                              Abort button selected                         vbAbort
4                                              Retry button selected                         vbRetry
5                                              Ignore button selected                        vbIgnore
6                                              Yes button selected                             vbYes
7                                              No button selected                              vbNo

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