CP2030 VBFC Lecture 4

CP2030 VBFCLecture 4

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Iteration - Looping Arrays

– Sliders– Arrays of user defined types

Controls - Frames, Radio Buttons, Check Boxes Controls - List, combo, picture, image, timer,

shape Data Validation

Looping Constructs

Looping constructs in Visual Basic: For...Next Loop

– used to perform a statement (or set of statements) a fixed number of times

– you should know how many times you want to perform the statements inside the loop before you reach the loop

Do...Loop– used to perform a statement (or set of

statements) one or more times, depending on whether the condition at the top or bottom of the loop is true or false

For...Next Loop Construct In C :

for (count=startvalue; condition; increment){

statements;

In VB ::Students to add syntax

Count can be any of these types: Integer or Long, Single or Double, Currency

For...Next Loop Step

We can also specify the step size and count backwards:

Sub Command1_Click ()Dim iCount As Integer For iCount = 100 To 0 Step -10 Print "iCount = "; iCount Next iCountEnd Sub

Unless a Step is specified the For loopwill increment by 1 each time

You should never change the value ofthe control variable inside the For loop

Do...Loop Forms There are a number of forms of the Do...Loop:

General form :

Do [{While / Until}] condition

statements

exitdo ‘can be used to terminate the loop

Loop same as break in C

statements

exitdo

Loop [{While/Until}] condition

Do While condition….Loop

1. Repeat while loop

Do While condition statementsLoop

Tests condition first Do While executes whilst the condition is

True, terminating when it becomes False Statements within looping structure are

only executed if the condition is true

Do...Loop Until condition

2. Repeat Until Loop

Do statementsLoop Until condition

Loop will always execute at least once.

Loop executes Until the condition is True,

Examples

Students to add example

Question

Write the equivalent C structures for :

(a) the repeat while loop

(b) the repeat until loop

Answers

Students to add answer

Refresh/DoEvents While in a loop VB directs all the computers

processing to calculations in the loop - can cause problems.

Refresh forces the object to be refreshed

eg. Lable1.Caption.Refresh

DoEvents forces checks on input from the user.

eg. DoEvents

Consider For inum=1 to 1000

label1.Caption=Str$(inum)

Arrays - Defining an Array Arrays can be delared for any type using

the standard declarations :Dim - at module, form or procedure

levelGlobal - at module levelStatic - at procedure level

Delaring the size of the array

Students to add examples

An array variable can be declared in a code module, a form, (or a procedure see later notes)

Accessing an Array

Array name and the element number are used

Dim asName(5) As String

asName(2) = “Pete”

asName(3) = “Lucy”

Text1.Text = asName(4)

(1) “Jane”

(3) “Lucy”

(2) “Pete”

(4) “Dave”

(5) “Ian”

asName

Array Bounds & Option Base

Arrays have a lower address or lower bound, and an upper address or upper bound

We can alter the default lower bound by using Option Base in the general declarations section of a form or module

Option Base can be set to either 0 or 1– Option Base 0 ‘sets the lower bound to 0– Option Base 1 ‘sets the lower bound to 1

Option Base 1

Option Base 0 asName 0 1 2 3 4

asName 51 2 3 4

Explicitly Stating Array Bounds

We can just declare how many elements we want in our array and Visual Basic will set them up using the Option Base setting:

We can however state explicitly the lower and upper bounds that we want for the array

Dim asName(5 To 9) As String

Option Base 1 asName 51 2 3 4

asName 95 6 7 8

Using Arrays in Applications

Let’s consider a simple application which stores up to 5 names:

Sub Command2_Click () Dim iPos As Integer iPos = Val(Text1.Text) If (iPos>=1) And (iPos<=5) Then Text2.Text = asNames(iPos) Else Text2.Text = "Error" End If Text1.SetFocusEnd Sub

Sub Command1_Click () Dim iPos As Integer iPos = Val(Text1.Text) If (iPos>=1) And (iPos<=5) Then asNames(iPos) = Text2.Text Else Text2.Text = "Error" End If Text1.SetFocusEnd Sub

Option Base 1Dim asNames(5) As String

In the form’s general declarations:

Multi-Dimensional Arrays

Visual basic will allow us up to 60 dimensions!

What about a three dimensional chess board?

Dim asBoard(1 To 8, 1 To 8, 1 To 8) As String

asBoard(1,4,3) = “White Knight”

We would advise you not to use too many dimensions, otherwise you will become confused

Best idea is only to use multi-dimensional arrays where they map clearly to the real-world

Clearing Arrays

To clear a complete array you can use the Erase command:

Students to add statement

This resets all fields to their ‘null’ values

Dynamic Arrays

Array size is allocated on demand

In the declaration Section: Dim asNames() As String

Within a procedure:

ReDim asNames(10)

ReDim Preserve asNames(15)

Finding Array Boundaries

To find the bounds of a single dimension array we can use:

iLowerBound = LBound( asNames )

iUpperBound = UBound( asNames )

To find multi-dimensional bounds:

Students to add statement

Question - Good Practice

Why is the following consider good practice?

Const NOOFSTUDS = 30

Dim Ages(NOOFSTUDS) As Integer

For icount=1 to NOOFSTUDS

iTotAges = iTotAges + Ages(icount)

Next icount

Data ValidationControls - Scroll Bars

There are two types of Scroll Bars Vertical & Horizontal

Main properties to set are: Max Min SmallChange LargeChange

Property usually retrieved is Value The events usually processed are Change

or Scroll– Change: when the position has changed message

is received– Scroll: when the thumbbar moves the message is

received

Question - arrays of records + Scroll bars

Telephone Data entered into the text boxes is to be written into a UDT array at an index given by the value of a scroll bar.

A scroll bar change event displays the data stored in the UDT array at the index given by the scroll bar value.

Show code

Controls: Option (Radio) Button

A Radio Button is one of thecontrols that can be used ona group frame

The property that we are usuallyinterested in is Value Option1.Value = FALSE Option1.Value = TRUE

Grouped Radio Buttons are mutually exclusive Can process on an Option Click event or wait for a command

event A Click event is automatically generated if you assign a value

to the Value property of an option from within a program

Controls: Radio Button Example Usage

Checking which option is selected:

Sub Command1_Click () If Option1.Value Then Label1.Caption = "Option1 Selected" ElseIf Option2.Value Then Label1.Caption = "Option2 Selected" ElseIf Option3.Value Then Label1.Caption = "Option3 Selected" Else Label1.Caption = "No Options Selected" End IfEnd Sub

Controls: Check Box 1

A Check Box is another control that can be used on a group frame:

Check Boxes can be control arrays

Check1.Value = 0 ’uncheckedCheck1.Value = 1 ’checked

Controls: Group Frame

Frames can be used to group sets of controls, both visually and programmatically:

The Click event can be used

When you place certain new controls on top of the frame they are automatically grouped together

If controls are not on a frame they are grouped on a form Radio Buttons can be control arrays

Group Frame Control

Controls: Check Box 2

The code behind the Show Checked command button would be:

Sub Command1_Click ()‘clear the label caption

Label1.Caption = ""‘add checked options to the label

If (Check1.Value) Then Label1.Caption=Label1.Caption+"Check1 Checked"+Chr(13) End If If (Check2.Value) Then Label1.Caption=Label1.Caption+"Check2 Checked"+Chr(13) End If If (Check3.Value) Then Label1.Caption=Label1.Caption+"Check3 Checked"+Chr(13) End IfEnd Sub

Controls : List and Combo Boxes

Used to select item(s) to be processes. Combo boxes open up when selected Combo boxes have an entry/edit area

List Box

A list box can be used to display & select items, it can be sorted

Items are stored in an array starting at index 0

Useful Methods:Students to add methods

List Box Useful Methods 1

AddItem adds the item specified to the List Box List1.AddItem “Item Text”

RemoveItem removes the item specified from the List Box List1.RemoveItem 1

Selected indicates if the specified item is currently selected List1.Selected(1)

ListIndex indicates the first selected item in the List Box iSelItem = List1.ListIndex

List Box Useful Methods 2

Clear clears all entries from the List Box List1.Clear

ListCount indicates how many items are currently in the List Box List1.ListCount

List is the array containing each of the items that are currently in the List Box Label1.Caption = List1.List(iCount)

Click is the event that is normally processed by the programmer

Combo Box

A combo box is like a list box that only displays the currently selected item, it drops down to allow selection, it can be sorted

Items are stored in an array starting at index 0

Useful Methods:Students to add methods

Comparing List box & Combo box

Occupies only one line on form when not in use.

Drop-down list appears when in use.

Can select from entries shown, or type in another value

Can select only one entry

Can display only one column

Occupies several lines on form at all times

Can select only from entries shown

Can select several items

Can display list in multiple columns

List box Combo box

Question

Write a section of code to add items to a list box under program execution - take the items from a text box.

Provide a count of the number of items in the list box

When an item is selected from the list box copy the item to a label box.

Picture, Image, Shape

Students to write notes on the above heading.

CP2030 VBFC Lecture 4

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