3/9/2004 PPCC - Introduction to VB6 Copyright ©2004, Tore Bostrup 1 Introduction to VB6 Week 2.

3/9/20043/9/2004PPCC - Introduction to VB6PPCC - Introduction to VB6

Copyright ©2004, Tore BostrupCopyright ©2004, Tore Bostrup 11

Introduction to VB6Introduction to VB6

Week 2Week 2


Copyright Copyright ©2004, Tore Bostrup©2004, Tore Bostrup Page 2

Review: The VB6 IDEReview: The VB6 IDE

The Forms DesignerThe Forms Designer The Toolbox window contains the The Toolbox window contains the

controls available for usecontrols available for use Double click an icon in the Toolbox orDouble click an icon in the Toolbox or Click an icon in the Toolbox and click and Click an icon in the Toolbox and click and

drag the sizing handles on the formdrag the sizing handles on the form Release the mouse buttonRelease the mouse button Resize control by selectingResize control by selecting

and click & drag sizing handlesand click & drag sizing handles



Review: The First App – Review: The First App – Hello WorldHello World

Open VB6Open VB6 Create a New Standard EXE projectCreate a New Standard EXE project Double-click the formDouble-click the form Enter the following code in Enter the following code in

Sub Form_Load()Sub Form_Load() MsgBox "Hello World"MsgBox "Hello World"

Press F5 or click the Press F5 or click the button button



Review: Hello World Review: Hello World VariationsVariations

Using constants and expressionsUsing constants and expressions Sub Form_Load()Sub Form_Load()

Const WORLD = "World"Const WORLD = "World" MsgBox "Hello " & WORLDMsgBox "Hello " & WORLD

End SubEnd Sub




Using Controls and VariablesUsing Controls and Variables Place a CommandButton on the formPlace a CommandButton on the form Add a Label, TextBox, and another Label to the Add a Label, TextBox, and another Label to the

formform Make the Caption for the first label "Name"Make the Caption for the first label "Name"

Double-click the ButtonDouble-click the Button Enter the following code in Enter the following code in

Sub CommandButton1_Click():Sub CommandButton1_Click(): Dim sHello as StringDim sHello as String sHello = "Hello " & Text1.TextsHello = "Hello " & Text1.Text Label2.Caption = sHelloLabel2.Caption = sHello

Press F5 to run, enter a name and click the buttonPress F5 to run, enter a name and click the button




This is what your form and code This is what your form and code should look like:should look like:



Hello World VariationsHello World Variations

What would make the last Hello What would make the last Hello World better?World better?



Hello World VariationsHello World Variations

What would make the last Hello What would make the last Hello World better?World better? Set the Text property for Text1 to an Set the Text property for Text1 to an

empty stringempty string Set the Caption property of the Set the Caption property of the

CommandButton to "Hello"CommandButton to "Hello"



Approximations of PIApproximations of PI

Sometimes it is useful to be able to Sometimes it is useful to be able to approximate the value of PI by using a approximate the value of PI by using a fraction.fraction. See See http://www.math.hmc.edu/funfacts/ffiles/10004.5.http://www.math.hmc.edu/funfacts/ffiles/10004.5.shtmlshtml

22 / 7 is a common simple fraction that 22 / 7 is a common simple fraction that produces PI with a result correct to 2 decimals produces PI with a result correct to 2 decimals (3.14)(3.14)

333 / 106 is good to 5 decimal places333 / 106 is good to 5 decimal places 355 / 113 is good for 6 decimal places355 / 113 is good for 6 decimal places To get a better result, we must use values To get a better result, we must use values

greater than 30,000.greater than 30,000.

http://www.math.hmc.edu/funfacts/ffiles/10004.5.shtml

http://www.math.hmc.edu/funfacts/ffiles/10004.5.shtml




Create a new Standard EXE projectCreate a new Standard EXE project Place three TextBoxes, three Labels Place three TextBoxes, three Labels

and a CommandButton on the form:and a CommandButton on the form:




Set the label Captions:Set the label Captions: Label1.Caption = "Dividend"Label1.Caption = "Dividend" Label2.Caption = "Divisor"Label2.Caption = "Divisor" Label3.Caption = "/"Label3.Caption = "/"

Clear the Text property of all the Clear the Text property of all the TextBoxes:TextBoxes:

Set the Caption for the Set the Caption for the CommandButtonCommandButton Command1.Caption = "PI ="Command1.Caption = "PI ="




After setting these and other After setting these and other properties (Form Caption, other…), properties (Form Caption, other…), your form should look something like your form should look something like thisthis




So let us add some code to the So let us add some code to the applicationapplication Double-click the button:Double-click the button:

Private Sub Command1_Click()Private Sub Command1_Click() Text3.Text = Text1.Text / Text2.TextText3.Text = Text1.Text / Text2.Text

Run the application (F5)Run the application (F5) Type 22 in the Dividend fieldType 22 in the Dividend field Type 7 in the Divisor fieldType 7 in the Divisor field Click on PI =Click on PI =



Behind the ScenesBehind the Scenes

What goes on behind the scenes in this What goes on behind the scenes in this simple statement?simple statement? A simple experiment: Change the line of code to:A simple experiment: Change the line of code to:

Text3.Text = Text1.Text Text3.Text = Text1.Text ++ Text2.Text Text2.Text Run the app (F5) and enter the same valuesRun the app (F5) and enter the same values You get 227!You get 227!

Because Text1.Text and Text2.Text are both Strings, the Because Text1.Text and Text2.Text are both Strings, the plus sign means CONCATENATE stringsplus sign means CONCATENATE strings

But with the original line of code, we got the But with the original line of code, we got the correct answer?correct answer?

Because VB is often (NOT ALWAYS) smart enough to know Because VB is often (NOT ALWAYS) smart enough to know that values must be converted to another type…that values must be converted to another type…



Behind the ScenesBehind the Scenes

Contd:Contd: But with the original line of code, we got the But with the original line of code, we got the

correct answer?correct answer? Because VB is often (NOT ALWAYS) smart enough to Because VB is often (NOT ALWAYS) smart enough to

know that values must be converted to another type…know that values must be converted to another type… REMEMBERREMEMBER

There is a difference between a string containing a There is a difference between a string containing a number and a numeric value. The same is true for number and a numeric value. The same is true for dates, etc.dates, etc.

Best PracticeBest Practice Perform Explicit Type ConversionsPerform Explicit Type Conversions




Back to our application – perform explicit Back to our application – perform explicit conversions, etc:conversions, etc: Double-click the button:Double-click the button:

Private Sub Command1_Click()Private Sub Command1_Click() Dim iDividend as IntegerDim iDividend as Integer Dim iDivisor as IntegerDim iDivisor as Integer Dim dblPI as DoubleDim dblPI as Double iDividend = Cint(Text1.Text)iDividend = Cint(Text1.Text) iDivisor = Cint(Text2.Text)iDivisor = Cint(Text2.Text) dblPI = iDividend / iDivisordblPI = iDividend / iDivisor Text3.Text = dblPIText3.Text = dblPI

Or:Or: Text3.Text = CDbl(Text1.Text) / Cint(Text2.Text)Text3.Text = CDbl(Text1.Text) / Cint(Text2.Text)



Type Conversion FunctionsType Conversion Functions

Each function coerces an Each function coerces an expressionexpression to a to a specific specific data typedata type.. CByte(expression), CInt(expression), CLng(expression)CByte(expression), CInt(expression), CLng(expression) CSng(expression), CDbl(expression)CSng(expression), CDbl(expression) CDec(expression), CCur(expression)CDec(expression), CCur(expression) CDate(expression)CDate(expression) CBool(expression)CBool(expression) CStr(expression), CVar(expression)CStr(expression), CVar(expression)

The required The required expressionexpression argumentargument is any is any string expressionstring expression or or numeric expressionnumeric expression..



Type Conversion FunctionsType Conversion Functions

Numeric – returns integer valuesNumeric – returns integer values CByte(expression), CInt(expression), CLng(expression)CByte(expression), CInt(expression), CLng(expression)

Numeric – returns floating point valuesNumeric – returns floating point values CSng(expression), CDbl(expression)CSng(expression), CDbl(expression)

Numeric – returns fixed decimal point valuesNumeric – returns fixed decimal point values CDec(expression), CCur(expression)CDec(expression), CCur(expression)

DateDate CDate(expression)CDate(expression)

Boolean (True/False)Boolean (True/False) CBool(expression)CBool(expression)

OtherOther CStr(expression), CVar(expression)CStr(expression), CVar(expression)




Try running the app again, but this Try running the app again, but this time don't type anything into the text time don't type anything into the text boxes:boxes:



Input ValidationInput Validation

This is an extremely common This is an extremely common problem with many applications:problem with many applications: Invalid input creates not only the wrong Invalid input creates not only the wrong

answer, but results in program errors!answer, but results in program errors! REMEMBERREMEMBER

ALWAYS validate input data!ALWAYS validate input data!




Let us add some validation code:Let us add some validation code: Double-click the buttonDouble-click the button

Add the following statements at the beginning ofAdd the following statements at the beginning ofPublic Sub Command1_Click() (after declarations):Public Sub Command1_Click() (after declarations):

If Trim$(Text1.Text) = "" ThenIf Trim$(Text1.Text) = "" Then MsgBox "You must specify a Dividend"MsgBox "You must specify a Dividend" Exit SubExit Sub

End IfEnd If If Trim$(Text2.Text) = "" ThenIf Trim$(Text2.Text) = "" Then

MsgBox "You must specify a Divisor"MsgBox "You must specify a Divisor" Exit SubExit Sub

End IfEnd If




Typical things to validateTypical things to validate Empty inputs (example "")Empty inputs (example "") Input that is only blank spaces (example Input that is only blank spaces (example

" ")" ") Input that will not convert to the correct Input that will not convert to the correct

data type (example "seven")data type (example "seven") Values that are not allowed (example: a Values that are not allowed (example: a

divisor of 0)divisor of 0)




Typical things to validateTypical things to validate Empty inputs and input that is only blank spaces Empty inputs and input that is only blank spaces

can be done in one testcan be done in one test The Trim$() function removes leading and trailing The Trim$() function removes leading and trailing

spacesspaces If Trim$(Text1.Text) = "" ThenIf Trim$(Text1.Text) = "" Then

Input that will not convert to the correct data typeInput that will not convert to the correct data type The IsNumeric() function checks if an expression can be The IsNumeric() function checks if an expression can be

evaluated as a Numeric valueevaluated as a Numeric value If Not IsNumeric(Text1.Text) ThenIf Not IsNumeric(Text1.Text) Then

Values that are not allowedValues that are not allowed If CInt(Text2.Text) = 0 thenIf CInt(Text2.Text) = 0 then




Real Input Validation codeReal Input Validation codeIf Trim$(Text1.Text) = "" Or Trim$(Text2.Text) = "" ThenIf Trim$(Text1.Text) = "" Or Trim$(Text2.Text) = "" Then

MsgBox "You must specify both Dividend and Divisor"MsgBox "You must specify both Dividend and Divisor"Exit SubExit Sub

ElseIf Not IsNumeric(Text1.Text) _ElseIf Not IsNumeric(Text1.Text) _ Or Not IsNumeric(Text2.Text) Then Or Not IsNumeric(Text2.Text) Then

MsgBox "Only Numeric values are allowed"MsgBox "Only Numeric values are allowed"Exit SubExit Sub

ElseElseIf CInt(Text2.Text) = 0 ThenIf CInt(Text2.Text) = 0 Then

MsgBox "You can't divide by 0"MsgBox "You can't divide by 0" Exit SubExit SubEnd IfEnd If

End IfEnd If



Accessing Controls on the Accessing Controls on the FormForm

In order to access a control on a In order to access a control on a form, we specify the name of the form, we specify the name of the control. Usually, we do this to access control. Usually, we do this to access one of the control's one of the control's propertiesproperties, so we , so we also specify the property following a also specify the property following a period:period: MsgBox "Hello " & Text1.TextMsgBox "Hello " & Text1.Text



Accessing Controls on the Accessing Controls on the FormForm

We can also use a fully qualified We can also use a fully qualified control name:control name: For instance Form1.Text1.TextFor instance Form1.Text1.Text The pseudo-variable Me is a reference to The pseudo-variable Me is a reference to

the form that the code belongs to:the form that the code belongs to: Me.Text1.TextMe.Text1.Text Typing Me. brings up all the available Typing Me. brings up all the available

properties and methods (procedures) for the properties and methods (procedures) for the form, including all the controls, allowing us to form, including all the controls, allowing us to type in a partial name or scroll through a list type in a partial name or scroll through a list of available selectionsof available selections



Properties, Methods, and Properties, Methods, and EventsEvents

We have already used both some We have already used both some Properties (Text1.Text, Properties (Text1.Text, Label1.Caption) Label1.Caption)

and some Events – or rather Event and some Events – or rather Event Procedures or Event Handlers Procedures or Event Handlers (Command1_Click(), Form1_Load())(Command1_Click(), Form1_Load())

But what are "Methods"?But what are "Methods"?



What are MethodsWhat are Methods

A Method is simply a procedure (Sub A Method is simply a procedure (Sub or Function) that exists in a form's or Function) that exists in a form's code (or in an object's code) that is code (or in an object's code) that is available* to be referenced.available* to be referenced.

* available to other code modules, objects, or * available to other code modules, objects, or applicationsapplications



Form and Control PropertiesForm and Control Properties

Forms and Controls have several Forms and Controls have several Properties - most of which can be Properties - most of which can be accessed and/or changed both during accessed and/or changed both during design and in code.design and in code.

Many form and control properties Many form and control properties describe visual aspects of the describe visual aspects of the form/controlform/control For example, a Label’s Caption property For example, a Label’s Caption property

determines what text it displaysdetermines what text it displays

3/9/2004 PPCC - Introduction to VB6 Copyright ©2004, Tore Bostrup 1 Introduction to VB6 Week 2.

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Transcript of 3/9/2004 PPCC - Introduction to VB6 Copyright ©2004, Tore Bostrup 1 Introduction to VB6 Week 2.