Microsoft Visual Basic 6 (Basic Programming Fundamental)

8/8/2019 Microsoft Visual Basic 6 (Basic Programming Fundamental)

http://slidepdf.com/reader/full/microsoft-visual-basic-6-basic-programming-fundamental 1/33

Basic Programming Fundamentals

Variable

A location in the computer's memory where data is stored. You can change the contents of avariable but its name and storage area are reserved for use until you end the Visual Basicsession or release the variable. Variables have a name (the word you use to refer), a data type(which determines the kind of data the variable can store) and value (to the value that variable

contains).

Scalar Variables and Array Variables

A variable containing a single value is a scalar variable. A variable that can contain more thanone related value to a single variable. This is called an array variable.

Variable Category

Category Name Description

Public/Global Variables declared using the Public Statement are visible to all procedures inall modules in all applications. not just the ones they are defined in.

Private/Local A variable that is accessible only within a function or procedure. Otherprocedures or functions cannot access this variable's data.

Variable LifetimeA term for a variable that continues to exist after a function call or program is finished. Publicand static variables continue to exist, local variables do not.

Scope of Variables

The range of reference for an object or variable . For example, local variables can bereferenced only within the procedure they were defined. Public variables are accessible fromanywhere in the application.

Scope Private Public

Procedure-level Variables are private to the procedure inwhich they appear.

Not applicable. You cannotdeclare public variables within aprocedure.

Module-level Variables are private to the module in which

they appear.

Variables are available to all

modules.




Visual Basic Data Types

Visual Basic classifies the information mentioned above into two major data types, they are thenumeric data types and the non-numeric data types.

Numeric Data Types

Numeric data types are types of data that consist of numbers, which can be computedmathematically with various standard operators. Examples of numeric data types areexamination marks, height, weight, the number of students in a class and etc.

Type Storage Range of Values

Byte 1 byte 0 to 255

Integer 2 bytes -32,768 to 32,767

Long 4 bytes -2,147,483,648 to 2,147,483,648

Single 4 bytes -3.402823E+38 to -1.401298E-45 for negative values

1.401298E-45 to 3.402823E+38 for positive values.Double 8 bytes -1.79769313486232e+308 to -4.94065645841247E-324 for negative values

4.94065645841247E-324 to 1.79769313486232e+308 for positive values.

Currency 8 bytes -922,337,203,685,477.5808 to 922,337,203,685,477.5807

Non-numeric Data Types

Nonnumeric data types are data that cannot be manipulated mathematically using standardarithmetic operators.

Data Type Storage Range

String(fixed length) Length of string 1 to 65,400 characters

String(variable length) Length + 10 bytes 0 to 2 billion characters

Date 8 bytes January 1, 100 to December 31, 9999

Boolean 2 bytes True or False

Object 4 bytes Any embedded object

Variant(numeric) 16 bytes Any value as large as Double

Variant(text) Length+22 bytes Same as variable-length string

Variable DeclarationDeclaring a variable means giving it a name, a data type and sometimes an initial value. Thedeclaration can be explicit or implicit.

Implicit Declaration

In implicit Variable declaration do not need to define variable type.Visual Basic adjust itstype according to the value you assign to it.Visual Basic use by default variable type isvariant.




Explicit Declaration

In Explicit Variable declaration you must define variable type.

Variable naming Conventions:• Must begin with an alphabetic character.• Can't contain an embedded period or type-declaration character.

• Must be unique within the same scope.• Must be no longer than 255 characters

Declaring Variables

Identifier variablename [As type ]

Identifier Description

Dim 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 theprocedure.

Private Private variables are available only to the module in which they are declared.

Public Variables declared using the Public statement are available to all procedures in allmodules in all applications

Global are available to all applications but Define in Module Level

Static Variables declared with the Static statement retain their values as long as the codeis running.

Example Dim bA As ByteDim bolA As BooleanDim iA,iB,iC As IntegerDim lA As LongDim sA As SingleDim dA As DoubleDim daA As DateDim oA As ObjectDim strA As String

Dim strfA As String * 20, Dim vA As Variant 'Depend on ValueStatic stA As Integer

Assigning Values to Variables

After declaring various variables using the Identifier, we can assign values to those variables.

The general format of an assignment is

Variable=ExpressionExample

bolA=TrueiA =100 : lA =100.35

strfA =”Karachi,Pakistan”




Converting Data Types

Visual Basic provides several conversion functions you can use to convert values into a specificdata type. To convert a value to Currency, for example, you use the CCur function:

PayPerWeek = CCur(hours * hourlyPay)

Conversion function Converts an expression to

Cbool BooleanCbyte Byte

Ccur Currency

Cdate Date

CDbl Double

Cint Integer

CLng Long

CSng Single

CStr StringCvar Variant

Constants

A constant is a meaningful name that takes the place of a number or string that does notchange. you can't modify a constant or assign a new value to it as you can to a variable. Thereare two sources for constants:

• Intrinsic or system-defined constants are provided by applications and controls. VisualBasic constants are listed in the Visual Basic (VB) and Visual Basic

• Symbolic or user-defined constants are declared using the Const statement

Creating Your Own ConstantsThe syntax for declaring a constant is:

[Public|Private] Const constantname [As type] = expression

Scoping User-Defined ConstantsA Const statement has scope like a variable declaration, and the same rules apply:

ExampleConst conPi = 3.14159265358979Public Const conMaxPlanets As Integer = 9

Const conReleaseDate = #01/01/2010#Public Const conVersion = "01.01.A"Const conCodeName = "Vista"




Operators in Visual Basic

To compute inputs from users and to generate results, we need to use various mathematicaloperators. In Visual Basic

Arithmetic and Text Operators

Operator Definition Example Result^ Exponent (power of) 4 ̂ 2 16

* Multiply 5 * 4 20

/ Divide 20 / 4 5

+ Add 3 + 4 7

- Subtract 7 - 3 4

Mod Remainder of division 20 Mod 6 2

\ Integer division 20 \ 6 3

& String concatenation "Karachi," & " " & "Pakistan" "Karachi, Pakistan"

Example

Dim number1, number2 AS Integer

Private sub Command1_Click

number1=val(Text1.Text) : number2=val(Text2.Text)

Label1.Caption= number1 ^ number2

Label2.Caption= number1 * number2 : Label3.Caption= number1 / number2

Label4.Caption= number1 + number2 : Label5.Caption= number1 - number2

Label6.Caption= number1 Mod number2

Label7.Caption= number1 \ number2Label8.Caption= Text1.Text & “ “ & Text2.Text

End Sub

Conditional Operators

To control the VB program flow, we can use various conditional operators. Basically, theyresemble mathematical operators. Conditional operators are very powerful tools, they let theVB program compare data values and then decide what action to take

Conditional Operators

Operator Definition Example Result= Equal to 9 = 11 False

> Greater than 11 > 9 True

< Less than 11 < 9 False

>= Greater or equal 15 >= 15 True

<= Less or equal 9 <= 15 True

<> Not equal 9 <> 9 False




Logical Operators

An operator that produces a logical result (true or false); sometimes called a Boolean operator.

Logical Operators

Operator Meaning Example Result

And Both sides must be true (9 = 9) AND (7 =6) False

or One side or other must be true (9 = 9) OR (7 = 6) True

Xor One side or other must be true but notboth

Not Negates truth Not (9=9) False

Introduction to Control Structures

Control structures allow you to control the flow of your program's execution. If left unchecked

by control-flow statements, a program's logic will flow through statements from left to right, andtop to bottom.

Decision Structures

Visual Basic procedures can test conditions and then, depending on the results of that test,perform different operations.

• If...Then• If...Then...Else• Select Case

If...ThenUse an If...Then structure to execute one or more statements conditionally. You can use either asingle-line syntax or a multiple-line block syntax:

Single-line Syntax

If condition Then statement

Multiple-line block Syntax

If condition1 Then[statementblock-1 ]

[ElseIf condition2 Then[statementblock-2 ]] ...

[Else[statementblock-n ]]

End IfThe condition is usually a comparison, but it can be any expression that evaluates to a numeric

value. Visual Basic interprets this value as True or False; a zero numeric value is False, and anynonzero numeric value is considered True. If condition is True, Visual Basic executes all thestatements following the Then keyword.




IF ...Then Examples

Private Sub cmdIF1_Click()a = 16If a > 10 Then a = a + 1: Print a

End Sub

Private Sub cmdIF3_Click()Dim number, digits As IntegerDim myString As String

number = InputBox("Please enter any

number.")

If number = "" Then Exit Sub

If number < 10 ThenmyString = "One"

ElseIf number >= 10 And number < 100 ThenmyString = "Two"

ElseIf number >= 100 And number < 1000

Then myString = "Three"Else

myString = "Un-Know"End If

If myString = "Un-Know" Then

Print myString & " number"Else

Print "You press " & myString & " digit

number"End IfEnd Sub

Private Sub cmdIF2_Click()Dim number, digits As IntegerDim myString As String

number = 53

If number < 10 Then

digits = 1Else

digits = 2

End If

If digits = 1 Then myString = "One digit"Else myString = "More than one digits"

Print myStringEnd Sub

Private Sub cmdIF4_Click()Dim Percantage As ByteClsfrmIF.FontSize = 15frmIF.BackColor = &H8000000FPercantage = InputBox("Enter your percantage to know grade.", "Grade Information")If Percantage >= 80 And Percantage <= 100 Then

frmIF.BackColor = vbGreenPrint "Your Grade is A+"Print "Percantage is " & Percantage & "%"

ElseIf Percantage >= 70 And Percantage < 80 ThenfrmIF.BackColor = vbBluePrint "Your Grade is A"Print "Percantage is " & Percantage & "%"

ElseIf Percantage >= 60 And Percantage < 70 ThenfrmIF.BackColor = vbYellowPrint "Your Grade is B"

Print "Percantage is " & Percantage & "%"




ElseIf Percantage >= 50 And Percantage < 60 ThenfrmIF.BackColor = &H8000000DPrint "Your Grade is C"Print "Percantage is " & Percantage & "%"

ElseIf Percantage >= 40 And Percantage < 50 ThenfrmIF.BackColor = &H80FF&

Print "Your Grade is D"Print "Percantage is " & Percantage & "%"

ElseIf Percantage >= 30 And Percantage < 40 ThenfrmIF.BackColor = &H40C0&Print "Your Grade is E"Print "Percantage is " & Percantage & "%"

ElsefrmIF.BackColor = vbRedPrint "Your Grade is Fail"Print "Percantage is " & Percantage & "%"

End IfEnd Sub

Select Case

A Select Case structure works with a single test expression that is evaluated once, at the top ofthe structure. Visual Basic then compares the result of this expression with the values for eachCase in the structure. If there is a match, it executes the block of statements associated withthat Case:

Syntax

Select Case testexpression[Case expressionlist1[statementblock-1]]

[Case expressionlist2[statementblock-2]]..

[Case Else[statementblock-n]]

End Select

Example

Private Sub cmdSC1_Click()Grade = InputBox("Enter your Grade.")Select Case UCase(Grade)

Case "A"MsgBox "Excellent"

Case "B"MsgBox "Good"

Case ElseMsgBox "Need Work Hard"

End Select

Private Sub cmdSC2_Click()age = InputBox("Enter your age")Select Case age

Case 18MsgBox "OOP! you young."

Case 35MsgBox "Sorry!you are not young."

End SelectEnd Sub




End Sub

Private Sub cmdSC3_Click()Dim mark As Singlemark = CSng(InputBox("Enter your

percentage"))

Select Case markCase Is >= 85

MsgBox "Excellence"Case Is >= 70

MsgBox "Good"Case Is >= 60

MsgBox "Above Average"Case Is >= 50

MsgBox "Average"Case Else

MsgBox "Need to work harder"End Select

End Sub

Private Sub cmdSC4_Click()Dim mark As Singlemark = CSng(InputBox("Enter your

percentage"))

Select Case markCase 0 To 49

MsgBox "Need to work harder"Case 50 To 59

MsgBox "Average"Case 60 To 69

MsgBox "Above Average"Case 70 To 84

MsgBox "Good"Case Else

MsgBox "Excellence"End Select

End Sub

Loop Structures

Loop structures allow you to execute one or more lines of code repetitively. The loopstructures that Visual Basic supports include:

• Do...Loop•

While …. Wend• For...Next• For Each...Next




Do...LoopUse a Do loop to execute a block of statements an indefinite number of times. There areseveral variations of the Do...Loop statement.

Loop zero or moretimes

Loop at least once Description

Do Until condition statements

Loop

Do statements

Loop Until condition

In the following Do...Until loop, thestatements execute as long as the condition is False

Do While condition

statements

Loop

Do statements

Loop Whilecondition

In the following Do...While loop, the

statements execute as long as the condition is True

Do...Until Examples

Private Sub cmdDoUntil1_Click()'Natural NumberDim x As IntegerClsx = 1Do Until x > 20

Print xx = x + 1

LoopEnd Sub

Private Sub cmdDoUntil2_Click()'Odd NumberDim x As IntegerClsx = 1Do Until x > 20

Print xx = x + 2

LoopEnd Sub

Private Sub cmdDoUntil3_Click()'Even NumberDim x As IntegerClsx = 2Do Until x > 20

Print xx = x + 2

LoopEnd Sub

Private Sub cmdDoUntil4_Click()'Table of 2Dim x As IntegerClsx = 1Do Until x > 10

Print "2 X" & x & "=" & 2 * xx = x + 1

LoopEnd Sub

Private Sub cmdDoUntil5_Click()'Get Table Number From Usertbl = InputBox("Enter table number which

you want to generate.", "Get Table Number")If tbl = "" Then Exit SubClsx = 1Do Until x > 10

Print tbl & "X" & x & "=" & tbl * x

x = x + 1

Private Sub cmdDoUntil6_Click()'Get Screen Font ListDim x As IntegerClsx = Screen.FontCountDo Until x = -1

Print Screen.Fonts(x)x = x - 1

Loop

End Sub




LoopEnd Sub

Private Sub cmdDoUntil7_Click()Dim x, y, z As Integer'Nested LoopCls

Print "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"x = 1Do Until x > 3

y = 1Do Until y > 3

z = 1Do Until z > 3

Print x; Space(5); y; Space(5); zz = z + 1

Loopy = y + 1

Loopx = x + 1

LoopEnd Sub

Loop...Until Examples

Private Sub cmdLoopUntil1_Click()'Natural Number

Dim x As IntegerClsx = 1Do

Print xx = x + 1

Loop Until x > 20End Sub

Private Sub cmdLoopUntil2_Click()'Odd Number

Dim x As IntegerClsx = 1Do

Print xx = x + 2


Private Sub cmdLoopUntil3_Click()'Even NumberDim x As IntegerClsx = 2Do

Print xx = x + 2


Private Sub cmdLoopUntil4_Click()'Table of 2Dim x As IntegerClsx = 1Do

Print "2 X" & x & "=" & 2 * xx = x + 1


Private Sub cmdLoopUntil5_Click()

'Get Table Number From User

Private Sub cmdLoopUntil6_Click()

'Get Screen Font List




tbl = InputBox("Enter table number which you want to generate.", "Get Table Number")

If tbl = "" Then Exit SubClsx = 1Do

Print tbl & "X" & x & "=" & tbl * xx = x + 1


Dim x As IntegerClsx = Screen.FontCountDo


Loop Until x = -1End Sub

Private Sub cmdLoopUntil7_Click()Dim x, y, z As Integer'Nested LoopClsPrint "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"

x = 1Do

y = 1Do

z = 1Do


Loop Until z > 3y = y + 1

Loop Until y > 3x = x + 1


Do...While Examples

Private Sub cmdDoWhile1_Click()'Natural NumberDim x As IntegerCls

x = 1Do While x <= 20

Print xx = x + 1

LoopEnd Sub

Private Sub cmdDoWhile2_Click()'Odd NumberDim x As IntegerCls


Print xx = x + 2

LoopEnd Sub

Private Sub cmdDoWhile3_Click()'Even NumberDim x As IntegerCls

Private Sub cmdDoWhile4_Click()'Table of 2Dim x As IntegerCls





Print xx = x + 2

LoopEnd Sub


Print "2 X" & x & "=" & 2 * xx = x + 1

LoopEnd Sub

Private Sub cmdDoWhile5_Click()'Get Table Number From Usertbl = InputBox("Enter table number which

you want to generate.", "Get Table Number")If tbl = "" Then Exit SubClsx = 1Do While x <= 10


LoopEnd Sub

Private Sub cmdDoWhile6_Click()'Get Screen Font ListDim x As IntegerClsx = Screen.FontCountDo While x <> 0


LoopEnd Sub

Private Sub cmdDoWhile7_Click()Dim x, y, z As Integer'Nested LoopClsPrint "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"x = 1Do While x <= 3

y = 1Do While y <= 3

z = 1Do While z <= 3


Loopy = y + 1

Loopx = x + 1

LoopEnd Sub

Loop...While Examples

Private Sub cmdLoopWhile1_Click()'Natural NumberDim x As Integer : Cls : x = 1Do

Print xx = x + 1

Private Sub cmdLoopWhile2_Click()'Odd NumberDim x As Integer : Cls : x = 1Do

Print xx = x + 2




Loop While x <= 20End Sub


Private Sub cmdLoopWhile3_Click()'Even NumberDim x As IntegerCls

x = 2Do

Print xx = x + 2


Private Sub cmdLoopWhile4_Click()'Table of 2Dim x As IntegerCls

x = 1Do

Print "2 X" & x & "=" & 2 * xx = x + 1


Private Sub cmdLoopWhile5_Click()'Get Table Number From Usertbl = InputBox("Enter table number which

you want to generate.", "Get Table Number")

If tbl = "" Then Exit SubClsx = 1Do



Private Sub cmdLoopWhile6_Click()'Get Screen Font ListDim x As IntegerCls

x = Screen.FontCountDo


Loop While x <> 0End Sub

Private Sub cmdLoopWhile7_Click()Dim x, y, z As Integer'Nested LoopClsPrint "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"x = 1Do

y = 1Do

z = 1Do


Loop While z <= 3y = y + 1

Loop While y <= 3x = x + 1





While ….. Wend Examples

Private Sub cmdWhileWend1_Click()'Natural NumberDim x As IntegerClsx = 1While x <= 20

Print xx = x + 1

WendEnd Sub

Private Sub cmdWhileWend2_Click()'Odd NumberDim x As IntegerClsx = 1While x <= 20

Print xx = x + 2

WendEnd Sub

Private Sub cmdWhileWend3_Click()'Even NumberDim x As IntegerCls

x = 2While x <= 20Print xx = x + 2

WendEnd Sub

Private Sub cmdWhileWend4_Click()'Table of 2Dim x As IntegerCls

x = 1While x <= 10Print "2 X" & x & "=" & 2 * xx = x + 1

WendEnd Sub

Private Sub cmdWhileWend5_Click()'Get Table Number From Usertbl = InputBox("Enter table number which

you want to generate.", "Get Table Number")

If tbl = "" Then Exit SubClsx = 1While x <= 10


WendEnd Sub

Private Sub cmdWhileWend6_Click()'Get Screen Font ListDim x As IntegerCls

x = Screen.FontCountWhile x <> 0


WendEnd Sub

Private Sub cmdWhileWend7_Click()Dim x, y, z As Integer

'Nested LoopClsPrint "--------------------------"Print "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"x = 1While x <= 3

y = 1While y <= 3

z = 1




While z <= 3Print x; Space(5); y; Space(5); zz = z + 1

Wendy = y + 1

Wend

x = x + 1Wend

End Sub

For...Next

When you know you must execute the statements a specific number of times, however, a For…Next loop is a better choice. Unlike a Do loop, a For loop uses a variable called a counter that

increases or decreases in value during each repetition of the loop. The syntax is:

For counter = start To end [Step increment]

statementsNext [counter]

For ….. Next Examples

Private Sub cmdFN1_Click()'Natural NumberClsFor x = 1 To 20

Print xNext x

End Sub

Private Sub cmdFN2_Click()'Odd NumberClsFor x = 1 To 20 Step 2

Print Tab(5); xNext

End Sub

Private Sub cmdFN3_Click()'Even NumberClsFor x = 2 To 20 Step 2

Print Tab(10); xNext x

End Sub

Private Sub cmdFN4_Click()'Generate Table of 2ClsFor x = 1 To 10

Print "2 X " & x & "=" & 2 * xNext x

End Sub

Private Sub cmdFN5_Click()

'Get Table Number From Usertbl = InputBox("Enter table number which you want to generate.", "Get Table Number")

If tbl = "" Then Exit SubClsFor x = 1 To 10

Print tbl & " X " & x & " = " & tbl * xNext x

End Sub


'Get Screen Font ListClsFor x = 1 To Screen.FontCount - 1

Print Screen.Fonts(x)Next x

End Sub





'Nested For LoopClsPrint "X"; Space(5); "Y"; Space(5); "Z"Print "--------------------------"For x = 1 To 3

For y = 1 To 3

For z = 1 To 3Print x; Space(5); y; Space(5); z

Next zNext y

Next xEnd Sub

For … Each

A For Each...Next loop is similar to a For...Next loop, but it repeats a group of statements for

each element in a collection of objects or in an array instead of repeating the statements aspecified number of times. This is especially helpful if you don't know how many elements are in acollection.

For Each element In groupstatements

Next element

For ….. Each Examples

Private Sub cmdFE1_Click()For Each ctl In frmIF.Controls

If TypeOf ctl Is TextBox Thenctl.BackColor = vbYellow

End IfNext ctl

End Sub

Exiting a Control Structure

The Exit statement allows you to exit directly from a Loop, Procedure, or Function procedure.

Exit Sub Exit From Procedure

Exit Function Exit From Function

Exit For Exit From For … Next Loop

Exit Do Exit From Do … While Loop




Introduction to Procedures

You can simplify programming tasks by breaking programs into smaller logical components. Thesecomponents called proceduresThere are two major benefits of programming with procedures:

• Procedures allow you to break your programs into discrete logical units, each of which

you can debug more easily than an entire program without procedures.• Procedures used in one program can act as building blocks for other programs, usually

with little or no modification.

Procedures Type

General ProceduresA general procedure tells the application how to perform a specific task. Once ageneral procedure is defined, it must be specifically invoked by the application.

Event ProceduresWhen an object in Visual Basic recognizes that an event has occurred, it

automatically invokes the event procedure using the name corresponding to the event.The syntax for a Sub procedure is:

[Private|Public][Static]Sub procedurename (arguments)statements

End Sub

Calling Procedures

A procedure differs from a Function procedure in that a Sub procedure cannot be called byusing its name within an expression. A call to a Sub is a stand-alone statement. Also, a Sub doesnot return a value in its name as does a function. However, like a Function, a Sub can modify the

values of any variables passed to it.There are two ways to call a Sub procedure:' Both of these statements call a Sub named MyProc.

Call MyProc (FirstArgument, SecondArgument)MyProc FirstArgument, SecondArgument

Note that when you use the Call syntax, arguments must be enclosed in parentheses. If you

omit the Call keyword, you must also omit the parentheses around the arguments.

Passing Arguments to Procedures

This information consists of variables passed to the procedure when it is called. When a

variable is passed to a procedure, it is called an argument .

Argument Data Types

The arguments for procedures you write have the Variant data type by default. However, youcan declare other data types for arguments.

ProcedureName (argumentName [AS type])




Example:

‘Declare ProcedurePrivate Sub Welcome()

Print"--------------------------------------------"

Print "Wellcome to Visual Basic 6"

Print"--------------------------------------------"End Sub

‘Declare ProcedurePublic Sub ApplicationTitle(frm As Object)

frm.Caption = "Inventory System " & NowEnd Sub

‘Calling ProcedurePrivate Sub cmdPro1_Click()

Call WelcomeEnd Sub


Call ApplicationTitle(frmProcedure)End Sub

Passing Arguments By Value

Only a copy of a variable is passed when an argument is passed by value. If the procedure

changes the value, the change affects only the copy and not the variable itself. Use the ByValkeyword to indicate an argument passed by value.

ProcedureName (ByVal argumentName [AS type])

Passing Arguments By Reference

Passing arguments by reference gives the procedure access to the actual variable contents inits memory address location. As a result, the variable's value can be permanently changed bythe procedure to which it is passed. Passing by reference is the default in Visual Basic.

ProcedureName (ByRef argumentName [AS type])

Using Optional ArgumentsYou can specify arguments to a procedure as optional by placing the Optional keyword in theargument list. If you specify an optional argument, all subsequent arguments in the argumentlist must also be optional and declared with the Optional keyword.

ProcedureName (Optional ByVal argumentName [AS type])

Providing a Default for an Optional Argument

It's also possible to specify a default value for an optional argument.

ProcedureName (Optional ByVal argumentName AS type=Value)

Using an Indefinite Number of Arguments

Generally, the number of arguments in the procedure call must be the same as in the procedure

specification. Using the ParamArray keyword allows you to specify that a procedure will accept

an arbitrary number of arguments. This allows you to write functions like Sum:

ProcedureName (ParamArray argumentName( ))

Creating Simpler Statements with Named Arguments

For many built-in functions, statements, and methods, Visual Basic provides the option of usingnamed arguments as a shortcut for typing argument values. With named arguments, you canprovide any or all of the arguments, in any order, by assigning a value to the named argument.You do this by typing the argument name plus a colon followed by an equal sign and the value




(MyArgument:= "SomeValue") and placing that assignment in any sequence delimited by

commas. This is especially useful if your procedures have several optional arguments that you donot always need to specify.

Example:

‘Declare With ByVal and Optional argumentPrivate Sub Power(ByVal x As Integer,

Optional ByVal y)If IsMissing(y) Then

y = 1End IfPrint (x ^ y)

End Sub

‘Declare With ByRef and Providing defaultvalue

Private Sub StringProcedure(ByRef pString AsString, ByRef a As Integer, Optional ByVal b AsInteger = 1)

pString = "After Calling String"a = 100b = 200

End Sub


Call Power(2)End Sub


Dim mystring As String, x As Integer, y AsInteger

mystring = "StartString"x = 10: y = 20Print "Before Calling Procedure": PrintPrint mystringPrint x: Print yPrint "----------------------------"Print "After Calling Procedure": PrintStringProcedure mystring, x, yPrint mystringPrint x: Print y

End Sub

‘Declare With ParamArrayPrivate Sub sum(ParamArray intsum())

For Each x In intsumy = y + x

NextPrint y

End Sub

‘Calling Procedure

Private Sub cmdPro5_Click()Call sum(1, 2, 3, 4, 5)

End Sub

‘Declare ProcedurePrivate Sub Total(ByVal x As Integer, OptionalByVal y As Integer = 0, Optional ByVal z AsInteger = 0)

Print x + y + zEnd Sub

‘Calling With Named argumentPrivate Sub cmdPro6_Click()

Call Total(10)Call Total(x:=10, z:=25)

End Sub

Introduction to Function Procedures

Visual Basic includes built-in, or intrinsic functions, like Sqr, Cos or Chr. In addition, you can usethe Function statement to write your own Function procedures.The syntax for a Function procedure is:

[Private|Public][Static]Function procedurename (arguments) [As type]statements

End Function




There are three differences between Sub and Function procedures:• Generally, you call a function by including the function procedure name and arguments on

the right side of a larger statement or expression (returnvalue = function() ).

• Function procedures have data types, just as variables do. This determines the type ofthe return value. (In the absence of an As clause, the type is the default Variant type.)

• You return a value by assigning it to the procedurename itself. When the Function

procedure returns a value, this value can then become part of a larger expression.• Function return value but sub procedure don’t return any value

Calling Function Procedures

Usually, you call a function procedure you've written yourself the same way you call an intrinsicVisual Basic function like Abs; that is, by using its name in an expression:

' All of the following statements would call a functionPrint 10 * FunctionNameX = FunctionNameIf FunctionName = 10 Then Debug.Print "Out of Range"X = AnotherFunction(10 * FunctionName)

Example:

'Function take no argument and no returnany valuePrivate Function ClearScreen()

ClsFor Each ctl In frmFunction.Controls

If TypeOf ctl Is TextBox Thenctl.Text = ""

End If

Next ctlEnd Function

'Function take argument and return valuePrivate Function Sum0(x As Integer, y AsInteger) As Double

Sum0 = x + yEnd Function

'Function take argument and return valueWith Optional argumentPrivate Function Sum1(a As Integer, b As

Integer, Optional c As Integer, Optional d AsInteger) As Double

Sum1 = a + b + c + dEnd Function

Private Sub cmdFun1_Click()Call ClearScreen

End Sub

'Function take argument and return valueWith Optional argument and assign defaultvaluePrivate Function Sum2(x As Integer, y AsInteger, Optional z As Integer = 1) As Double

Sum2 = x + y + zEnd Function

Private Sub cmdFun2_Click()MsgBox Sum0(100, 50)MsgBox Sum2(10, 20)

End Sub

Private Sub cmdFun2_Click()MsgBox Sum1(50, 50, 60)MsgBox Sum1(a:=10, b:=20, d:=15)

End Sub

'Function take argument and return value

Public Function Min(ByVal x As Double, ByVal yAs Double) As Double

If x > y Then

Min = y

'Function take argument and return value

Public Function Max(ByVal x As Double, ByVal yAs Double) As Double

If x > y Then

Max = x




ElseMin = x

End IfEnd Function

ElseMax = y

End IfEnd Function

Function take argument but no return any

value using ByValPrivate Function FunByVal(ByVal x As Integer)

x = x + 5End Function

'Function take argument but no return any

value using ByRefPrivate Function FunByRef(ByRef x As Integer)

x = x + 5End Function

Private Sub cmdFun5_Click()Dim v1 As Integerv1 = 30Print v1Call FunByVal(v1)Print v1

End Sub

Private Sub cmdFun4_Click()Dim v1 As Integerv1 = 30Print v1Call FunByRef(v1)Print v1

End Sub

Calling Sub Procedures/Function Procedures in Other Modules

Public procedures in other modules can be called from anywhere in the project. You might needto specify the module that contains the procedure you're calling. The techniques for doing thisvary, depending on whether the procedure is located in a form, class, or standard module.

Sub Procedures/Function Procedures in Forms

All calls from outside the form module must point to the form module containing the procedure.If a procedure named SomeSub is in a form module called Form1, then you can call the

procedure in Form1 by using this statement:Call Form1.SomeSub(arguments)

Sub Procedures/Function Procedures in Class Modules

Like calling a procedure in a form, calling a procedure in a class module requires that the call tothe procedure be qualified with a variable that points to an instance of the class. For example,DemoClass is an instance of a class named Class1:

Dim DemoClass as New Class1DemoClass.SomeSub

Sub Procedures/Function Procedures in Standard Modules

If a procedure name is unique, you don't need to include the module name in the call. A call frominside or outside the module will refer to that unique procedure. A procedure is unique if itappears only in one place.If two or more modules contain a procedure with the same name, youmay need to qualify it with the module name. A call to a common procedure from the samemodule runs the procedure in that module. For example, with a procedure named CommonNamein Module1 and Module2, a call to CommonName from Module2 will run the CommonNameprocedure in Module2, not the CommonName procedure in Module1.A call to a common procedurename from another module must specify the intended module. For example, if you want to callthe CommonName procedure in Module2 from Module1, use:

Module2.CommonName(arguments)




Introduction to Arrays

An array is a list of variables, all with the same data type and name. When we work with a singleitem, we only need to use one variable. However, if we have a list of items which are of similartype to use array. Arrays have both upper and lower bounds, and the elements of the array arecontiguous within those bounds. Because Visual Basic allocates space for each index number,avoid declaring an array larger than necessary.

In Visual Basic there are two types of arrays:

• A fixed-size array which always remains the same size.

• A dynamic array whose size can change at run-time.

The format for declaring an array is:

Dim|Public|Private ArrayName([Subscript], [Subscript], [Subscript]) [As DataType]

- Dim, Public, and Private declare the array and its scope.- ArrayName is the name of the array.- Subscript is the dimensions of the array.- DataType is any valid data type.

Declaring Fixed-Size Arrays

The general format to declare a one/Single dimensional array is as follow:

Dim|Public|Private arrayName(Subscript) as dataType

The general format to declare a Multidimensional /two dimensional array is as follow:

Dim|Public|Private ArrayName(Subscript, Subscript) as dataType

The general format to declare a Multidimensional /three dimensional array is as follow:

Dim|Public|Private ArrayName(Subscript, Subscript, Subscript) as dataTypeExample of Single /One dimensional array

Private Sub cmdArray1_Click()'Declare ArrayDim StudentName(4) As String'Assign Data to Array ElementStudentName(0) = "Arshed Khan"StudentName(1) = "Amir Khan"StudentName(2) = "Ahmed Ansari"

StudentName(3) = "Gulzar Ahmed"StudentName(4) = "Mohammad Ali"'Access Array ElementPrint StudentName(0)Print StudentName(1)Print StudentName(2)Print StudentName(3)Print StudentName(4)

End Sub

Private Sub cmdArray2_Click()'Declare ArrayDim StudentName(1 To 5) As String'Assign Data to Array ElementStudentName(1) = "Arshed Khan"StudentName(2) = "Amir Khan"StudentName(3) = "Ahmed Ansari"

StudentName(4) = "Gulzar Ahmed"StudentName(5) = "Mohammad Ali"'Access Array ElementPrint StudentName(1)Print StudentName(2)Print StudentName(3)Print StudentName(4)Print StudentName(5)

End Sub




Private Sub cmdArray3_Click()'Declare ArrayDim StudentName(4) As String'Assign Data to Array ElementFor x = 0 To 4

StudentName(x) = InputBox("Enter

Student Name.")Next x'Access Array ElementFor x = 0 To 4

Print StudentName(x)Next x

End Sub

Private Sub cmdArray4_Click()'Declare ArrayDim StudentName(1 To 5) As String'Assign Data to Array ElementFor x = 1 To 5

StudentName(x) = InputBox("Enter

Student Name.")Next x'Access Array ElementFor x = 1 To 5


End Sub

Example of Multidimensional / Two dimensional array

Private Sub cmdArray5_Click()

'Declare ArrayDim StudentName(3, 1) As String'Assign Data to Array ElementStudentName(0, 0) = "1001"StudentName(0, 1) = "Arshed Khan"StudentName(1, 0) = "1002"StudentName(1, 1) = "Amir Khan"StudentName(2, 0) = "1003"StudentName(2, 1) = "Ahmed Ansari"StudentName(3, 0) = "1004"

StudentName(3, 1) = "Gulzar Ahmed"'Access Array ElementPrint "Code " & "Name "Print "------------------------"Print StudentName(0, 0) & " " &

StudentName(0, 1)Print StudentName(1, 0) & " " &


StudentName(2, 1)

Print StudentName(3, 0) & " " &StudentName(3, 1)End Sub


'Declare ArrayDim StudentName(3, 1) As String'Assign Data to Array ElementFor x = 0 To 3

For y = 0 To 1If y = 0 Then

StudentName(x, y) = InputBox("EnterStudent Code:")

ElseStudentName(x, y) = InputBox("Enter

Student Name:")End If

Next yNext x'Access Array ElementPrint "Code " & "Name "Print "------------------------"For x = 0 To 3

Print StudentName(x, 0) & " " &StudentName(x, 1)

Next xEnd Sub




Example of Multidimensional / Three dimensional array

Private Sub cmdArray7_Click()'Declare ArrayDim StudentName(1 To 2, 1 To 4, 1 To 3) As String'Assign Data to Array Element

StudentName(1, 1, 1) = "9-A"StudentName(1, 1, 2) = "1001"StudentName(1, 1, 3) = "Arshed Khan"StudentName(1, 2, 1) = "9-A"StudentName(1, 2, 2) = "1002"StudentName(1, 2, 3) = "Amir Khan"StudentName(1, 3, 1) = "9-A"StudentName(1, 3, 2) = "1003"StudentName(1, 3, 3) = "Ahmed Ansari"StudentName(1, 4, 1) = "9-A"

StudentName(1, 4, 2) = "1004"StudentName(1, 4, 3) = "Gulzar Ahmed"StudentName(2, 1, 1) = "9-B"StudentName(2, 1, 2) = "1001"StudentName(2, 1, 3) = "SANA"StudentName(2, 2, 1) = "9-B"StudentName(2, 2, 2) = "1002"StudentName(2, 2, 3) = "HINA"StudentName(2, 3, 1) = "9-B"StudentName(2, 3, 2) = "1003"

StudentName(2, 3, 3) = "HUMA"StudentName(2, 4, 1) = "9-B"StudentName(2, 4, 2) = "1004"StudentName(2, 4, 3) = "RABIA"'Access Array ElementPrint "Class " & "Code " & "Name "Print "-----------------------------------------"Print StudentName(1, 1, 1) & " " & StudentName(1, 1, 2) & " " & StudentName(1, 1, 3)Print StudentName(1, 2, 1) & " " & StudentName(1, 2, 2) & " " & StudentName(1, 2, 3)Print StudentName(1, 3, 1) & " " & StudentName(1, 3, 2) & " " & StudentName(1, 3, 3)

Print StudentName(1, 4, 1) & " " & StudentName(1, 4, 2) & " " & StudentName(1, 4, 3)Print "-----------------------------------------"Print StudentName(2, 1, 1) & " " & StudentName(2, 1, 2) & " " & StudentName(2, 1, 3)Print StudentName(2, 2, 1) & " " & StudentName(2, 2, 2) & " " & StudentName(2, 2, 3)Print StudentName(2, 3, 1) & " " & StudentName(2, 3, 2) & " " & StudentName(2, 3, 3)Print StudentName(2, 4, 1) & " " & StudentName(2, 4, 2) & " " & StudentName(2, 4, 3)

End Sub




Private Sub cmdArray8_Click()'Declare ArrayDim StudentName(1 To 2, 1 To 4, 1 To 3) As String'Assign Data to Array ElementFor x = 1 To 2

For y = 1 To 4

For z = 1 To 3If z = 1 Then

StudentName(x, y, z) = InputBox("Enter Student Class:")ElseIf z = 2 Then

StudentName(x, y, z) = InputBox("Enter Student Code:")Else

StudentName(x, y, z) = InputBox("Enter Student Name:")End If

Next zNext y

Next x'Access Array ElementFor x = 1 To 2

Print "Class " & "Code " & "Name "Print "-----------------------------------------"For y = 1 To 4

Print StudentName(x, y, 1) & " " & StudentName(x, y, 2) & " " & StudentName(x, y, 3)Next y

Next xEnd Sub




Example of Array of arrays

Private Sub cmdArray9_Click()'Declare ArrayDim StudentName9ACode(1 To 3) As IntegerDim StudentName9AName(1 To 3) As String

Dim Class9(1 To 2) As Variant'Assign Data to Array ElementFor x = 1 To 3

StudentName9ACode(x) = InputBox("EnterStudent Code:")

StudentName9AName(x) =InputBox("Enter Student Name:")

Next xClass9(1) = StudentName9ACode()Class9(2) = StudentName9AName()

'Access Array ElementPrint "Code " & "Name "Print "----------------"For x = LBound(StudentName9ACode) To

UBound(StudentName9ACode)Print Class9(1)(x) & " " & Class9(2)(x)

Next xEnd Sub

Private Sub cmdArray10_Click()Dim StudentName As VariantDim sNameStudentName = Array("Arshed", "Ali",

"Amir", "Gulzar")For x = 0 To 3Print StudentName(x)

Next xEnd Sub

Private Sub cmdArray11_Click()Dim Serial(4) As StringIf IsArray(Serial) Then

For x = LBound(Serial) To UBound(Serial)Serial(x) = x

Next xEnd IfIf IsArray(Serial) Then

For x = LBound(Serial) To UBound(Serial)Print Serial(x)

Next xPrint "Your array have been erased."Erase Serial

End IfEnd Sub

IsArray Test the variable type

Array Used to assign multiple values in one statement

Option Base Set the default lower index limit

LBound | UBound Determine the upper and lower bounds of the specifieddimension

Erase Clear the array's contents

Redim Change the size of the array at runtime

Preserve optional keyword that forces Visual Basic to retain all existingelements' values

Dim | Private | Public | Static Declare the array




Declaring Dynamic Arrays

The ReDim statement is used to size or resize a dynamic array that has already been formallydeclared using a Private, Public, or Dim statement with empty parentheses (without dimensionsubscripts).

The ReDim keyword's syntax is:

ReDim [Preserve] ArrayName(Subscript) As DataType

- ReDim is the keyword that denotes we are redimensioning an array.- Preserve is an optional keyword that forces Visual Basic to retain all existingelements' values. If you use the Preserve keyword, you can resize only the last arraydimension and you can't change the number of dimensions at all.

Example of Dynamic Array

Private Sub cmdArray12_Click()Dim StudentName() As String

NofStudent = InputBox("How many Student in your class?")ReDim StudentName(Val(NofStudent))For x = 0 To UBound(StudentName)

StudentName(x) = InputBox("Enter Student Name")Next xFor x = 0 To UBound(StudentName)


End Sub


Dim StudentName() As StringReDim StudentName(1, 1) As StringStudentName(0, 0) = "1001"StudentName(0, 1) = "Ali"StudentName(1, 0) = "1002"StudentName(1, 1) = "Arshed"Print StudentName(0, 0) & " " &


StudentName(1, 1)

ReDim Preserve StudentName(1, 0To UBound(StudentName) + 1) AsString

StudentName(1, 0) = "1001"StudentName(1, 1) = "Ali"StudentName(1, 2) = "Class 9A"

:PrintPrint StudentName(0, 0) & " " &


StudentName(1, 1) & " " &


Dim strStudentNames() As StringDim strText As StringDim blDimensioned As BooleanDim lngPosition As LongDo

strText = InputBox("Enter a Student name:")If strText <> "" Then

If blDimensioned = True Then'Yes, so extend the array one element large

than its current upper bound.

ReDim Preserve strStudentNames(0 ToUBound(strStudentNames) + 1) As String

Else'No, so dimension it and flag it as

dimensioned.ReDim strStudentNames(0 To 0) As StringblDimensioned = True

End If'Add the Student Name to the last element in

the array.

strStudentNames(UBound(strStudentNames)) =




StudentName(1, 2)ReDim StudentName(2, 1) As StringStudentName(0, 0) = "1001"StudentName(0, 1) = "Ali"StudentName(1, 0) = "1002"StudentName(1, 1) = "Arshed"

StudentName(2, 0) = "1003"StudentName(2, 1) = "Gulzar" :PrintPrint StudentName(0, 0) & " " &



StudentName(2, 1)End Sub

strTextEnd If

Loop Until strText = ""'Display entered Student names:For lngPosition = LBound(strStudentNames) To

UBound(strStudentNames)

Print strStudentNames(lngPosition)Next lngPosition'Erase arrayErase strStudentNames

End Sub

User-Defined Data Types

Variables of different data types when combined as a single variable to hold several relatedinformations is called a User-Defined data type.A Type statement is used to define a user-defined type in the General declaration section of a form or module. User-defined data typescan only be private in form while in standard modules can be public or private.The Typedefinition is basically a "template" on which other variables are defined; the template itselfdoes not store any data. To use a UDT, you must define a variable

The syntax for defining a UDT is:

[Public | Private] Type TypeNameVariable1 As datatype...Variablen As datatype

End Type

The following rules apply to UDTs:

• UDTs declared only at the module-level (Do not declare a UDT in an individual Sub orFunction)

• UDTs may have Public (project-level) or Private (module-level) scope. The default is

Public.• UDTs with Public scope may only be defined in standard modules, not forms.

Example

Private Type EmpNameFirstName As StringLastName As String

End Type

Private Type EmpRecord

empCode As Integer

Private Sub cmdType1_Click()Dim empRec As EmpRecordempRec.empCode = "1001"empRec.EmpName.FirstName = "Ahmed"empRec.EmpName.LastName = "Ali"empRec.empSalary = 2500

Print "Employee Code :" & empRec.empCode




EmpName As EmpNameempSalary As CurrencySalaryMonth(12) As String

End Type

Print "Employee Name :" &empRec.EmpName.FirstName & " " &empRec.EmpName.LastName

Print "Employee Salary :" & empRec.empSalaryEnd Sub

‘UDT with Array

Private Sub cmdType2_Click()Dim EmpRec(4) As EmpRecordFor x = 0 To 4

EmpRec(x).EmpCode = InputBox("Enter Code")EmpRec(x).EmpName.FirstName = InputBox("Enter Name")EmpRec(x).EmpSalary = InputBox("Enter Salary")EmpRec(x).SalaryMonth(1) = "Jan"

Next xFor x = 0 To 4

Print EmpRec(x).EmpCode & " " & EmpRec(x).EmpName.FirstName & " " &

EmpRec(x).EmpSalary & " " & EmpRec(x).SalaryMonth(1)Next x

End Sub

Example UDT With Sub Procedure and Function Procedure

‘StructurePrivate Type InventoryItem

Item_Code As StringItem_Name As StringItem_Desc As String

Item_Price As DoubleItem_Qty As Integer

End Type‘ProcedurePrivate Sub Itemlist(itemRec AsInventoryItem)

Debug.Print "Item Code " & "Item Name " &"Item Description " & "Qty " & "Price " &"Amount"

Debug.Print itemRec.Item_Code & " " &

itemRec.Item_Name & " " &itemRec.Item_Desc & " " &itemRec.Item_Price & " " & itemRec.Item_Qty& " " & itemRec.Item_Qty *itemRec.Item_PriceEnd Sub‘FunctionPrivate Function getItemlist() AsInventoryItem

Dim item As InventoryItem

‘Call Procedure and FunctionPrivate Sub cmdType3_Click()

Dim item As InventoryItemitem.Item_Code = "1001"item.Item_Name = "Pen (Pointer)"

item.Item_Desc = "Pen use for dark writing"item.Item_Price = 18item.Item_Qty = 36

'Call Procedure and pass parameterCall Itemlist(item)

'Call Function and get parameterPrint "Item Code " & getItemlist().Item_CodePrint "Item Name " &

getItemlist().Item_NamePrint "Item Description " &

getItemlist.Item_DescPrint "Item Qty " & getItemlist.Item_QtyPrint "Item Price " & getItemlist.Item_PricePrint "Total Amount " &

getItemlist().Item_Qty *getItemlist().Item_PriceEnd Sub




item.Item_Code = "1002"item.Item_Name = "Book 1 (English Poem)"item.Item_Desc = "Book for class 1"item.Item_Price = 57item.Item_Qty = 50getItemlist = item

End Function

Enums (enumerations)

Enums (enumerations) are structures you define when you need a set of constant values. AnEnum must be declared outside of any Sub Procedure and Function body. The elements of theEnum type are initialized to constant values within the Enum statement. The assigned valuescan't be modified at run time and can include both positive and negative numbers. the firstconstant in an enumeration is initialized to the value 0, and subsequent constants are initializedto the value of one more that the previous constant.

Syntax

[Public | Private] Enum name

membername [= constantexpression]membername [= constantexpression]. . .

End Enum

Example

Private Enum DaysNameMonday = 1Tuesday = 2Wednesday = 3Thursday = 4Friday = 5Saturday = 6Sunday = 7

End Enum

Private Sub cmdEnum_Click()Print DaysName.FridayPrint CalculateHourTime(Sunday)

End SubPrivate Function CalculateHourTime(day AsDaysName)

If day = Sunday ThenPrint "No any Hour Time allow on Sunday."

ElsePrint "Calculation of Hour Time"

End IfEnd Function




Collection

A collection is a way of grouping a set of related items. Collections are used in Visual Basic tokeep track of many things, such as the loaded forms in your program (the Forms collection), orall the controls on a form (the Controls collection).Visual Basic provides the generic Collectionclass to give you the ability to define your own collections. You can create as many Collection

objects — that is, instances of the Collection class. Each Collection object comes withproperties and methods you can use to insert, delete, and retrieve the items in the collection.

Property or method Description

Add method Add items to the collection.

Count property Return the number of items in the collection. Read-only.

Item method Return an item, by index or by key.

Remove method Delete an item from the collection, by index or by key.

Example

Private Sub cmdCollection1_Click()'Create object variable for collectionDim itm As New Collection'Add value in collectionitm.Add ("A")itm.Add ("B")itm.Add ("c")itm.Add ("d")'Count number of item in collection

Print itm.Count'Retrive item from collectionPrint itm.item(2)Print itm(3)'Remove item from collectionitm.Remove (2)Print itm.Count

End Sub

‘Control CollectionPrivate Sub cmdCollection2_Click()

For Each ctl In frmCollection.ControlsIf TypeOf ctl Is TextBox Then

ctl.Text = ""End If

Next ctlEnd Sub

Microsoft Visual Basic 6 (Basic Programming Fundamental)

Documents

Transcript of Microsoft Visual Basic 6 (Basic Programming Fundamental)