Flow Control II

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Flow Control II

Code: Select-Case and For-NextControls: Frames and OptionButtons

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OptionButtons

A.k.a. Radio Buttons Used if one and only one choice must be made The one and only one logic is built into the radio

button controls The default method on an OptionButton is

associated with the click event; it tells one that that particular choice was most recently selected

Important property: value: Boolean determines if that buttons was the one selected (true)

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BackColor Selection

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BackColor Selection

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BackColor Selection

Option Explicit

Private Sub optBlue_Click() frmSelectColor.BackColor = vbBlueEnd Sub

Private Sub optGreen_Click() frmSelectColor.BackColor = vbGreenEnd Sub

Private Sub optCyan_Click() frmSelectColor.BackColor = vbCyanEnd Sub

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BackColor Selection (Extended)

optRed’s value property was set to true during development

but the backcolor is assigned only on a click event

One could have another method (e.g. Form_Load) call optRed_Click whichj will give the same effect as if optRed had been clicked

(Note each optionbutton has its own backcolor property, they remain default gray in this example)

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BackColor Selection (Extended)

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Multiple choice

From a group of OptionButtons, one and only one can have a true value

But what if there are a number of categories, and the user must choose one item from each category

We have to let the program know which optionbuttons belong to a group

This is done with frames

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Frame

Recall a form provides a surface or container for controls

A frame is like a form within a form (a container within a container) It groups controls together, so that

can be treated as a separate set Often used if there is more than one

set of radio buttons

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Putting OptionButtons in Frames

Make the Frame first, then put the new OptionButton in it; if you move a pre-existing OptionButton into a Frame, it’s not really in the Frame

If you use copy and paste to make additional OptionButtons, be sure that the Frame is highlighted before clicking paste (also at this stage we do not want a control array)

To move a pre-existing OptionButton into a Frame, cut it and paste it into the Frame

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Multiple Choice Example

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Option Explicit

Private Sub opt12_Click() txtText.FontSize = 12End Sub



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Private Sub optArial_Click() txtText.FontName = "Arial"End Sub

Private Sub optCourier_Click() txtText.FontName = "Courier"End Sub

Private Sub optTimes_Click() txtText.FontName = "Times New Roman"End Sub

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Select-Case

The Select-Case statement is a fancy version of the If-Then structure used when there are several branches of the algorithm that might be taken and which branch is determined by a single expression

P. 140 in Deitel, Deitel and Nieto

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Other uses of Frames

Frames are good for grouping controls That might be moved together That might be “disabled” together That might be made “invisible”

together Etc.

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Right Justified Frame

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Const MARGIN As Integer = 200

Private Sub Form_Resize() fraFontSize.Left = frmFonts.ScaleWidth - _

fraFontSize.Width - MARGINEnd Sub

‘don’t need to move optionbuttons just the ‘frame containing them

Using Const instead of Dimmeans the number cannot be changed later on

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State Tax Example

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State Tax Example

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State Tax Example

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State Tax Example

Private Sub cmdCalculate_Click() Select Case UCase(txtState.Text) Case Is = "PA" txtTotal.Text = txtSubTotal.Text * 1.06 Case Is = "CA" txtTotal.Text = txtSubTotal.Text * 1.0875 Case Is = "MA" txtTotal.Text = txtSubTotal.Text * 1.0725 Case Else txtTotal.Text = txtSubTotal.Text End SelectEnd Sub Capitalizes a string

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Select Case Flexibility

In Visual Basic the Select-Case statement allows for cases that are Inequalities (e.g. Case Is < 4) Ranges (e.g. Case 53 To 64) Comma separated values (e.g. Case

Is 75, 99, 302) The corresponding statement in

other languages is not as flexible

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Arithmetic Homework Revisited

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Option ExplicitDim Number1 As IntegerDim Number2 As Integer

'----------------------------------------------------Private Sub optAdd_Click() cmdSymbol.Caption = "+" txtResult.Text = ""End Sub

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Private Sub optMultiplication_Click() cmdSymbol.Caption = "*" txtResult.Text = ""End Sub

'----------------------------------------------------Private Sub optSubtract_Click() cmdSymbol.Caption = "-" txtResult.Text = ""End Sub

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Private Sub txtNumber1_Validate(Cancel As Boolean)

If IsNumeric(txtNumber1.Text) Then Number1 = CInt(txtNumber1.Text) Else MsgBox ("Please enter a number.") txtNumber1.Text = "" Cancel = True End IfEnd Sub

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Private Sub txtNumber2_Validate(Cancel As Boolean)

If IsNumeric(txtNumber2.Text) Then Number2 = CInt(txtNumber2.Text) Else MsgBox ("Please enter a number.") txtNumber2.Text = "" Cancel = True End IfEnd Sub

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Private Sub cmdSymbol_Click() Select Case cmdSymbol.Caption Case "+" txtResult.Text = Number1 + Number2 Case "-" txtResult.Text = Number1 - Number2 Case "*" txtResult.Text = Number1 * Number2 Case Else MsgBox ("Something is wrong.") End SelectEnd Sub

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Private Sub cmdClear_Click() txtNumber1.Text = "" txtNumber2.Text = "" txtResult.Text = "" txtNumber1.SetFocusEnd Sub

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For-Next Loop

One of the structures used for repeating steps

A condition is tested, specifically whether a counter falls within some limit If the condition is true, the statements in the for-

next block are executed, at the “bottom” the counter is incremented, and one returns to the “top” of the loop to test the condition again

If the condition is false, the for-next statements are not executed and the next statement executed is the one following Next

P. 132 in Deitel, Deitel and Nieto

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Accumulating Interest

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Private Sub cmdCalculate_Click() Dim Year As Integer Dim Balance As Currency Dim Rate As Double Balance =

CDbl(txtInitialAmount.Text) Rate = CDbl(txtRate.Text) / 100

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txtBalance.Text = "" For Year = 1 To CInt(txtLife.Text) Balance = Balance * (1 + Rate) txtBalance.Text = txtBalance.Text & Year

& _ vbTab & "$" & Balance & vbCrLf Next YearEnd Sub

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Step

To change the counter by anything other than 1, use the keyword Step to indicate the amount by which the counter should be incremented

For example, For I=10 to 0 Step –1

begins a loop that counts backwards

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Quarterly Interest

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Quarterly Interest

Private Sub cmdCalculate_Click() Dim Year As Single Dim Balance As Currency Dim Rate As Double Balance =

CDbl(txtInitialAmount.Text) Rate = CDbl(txtRate.Text) / 100 / 4

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Quarterly Interest

txtBalance.Text = "" For Year = 0.25 To CInt(txtLife.Text) Step

0.25 Balance = Balance * (1 + Rate) txtBalance.Text = txtBalance.Text & Year &

_ vbTab & "$" & Balance & vbCrLf Next YearEnd Sub

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Style Notes

Indent all statements within a method

Indent all statements within an If-Then-Else structure

Indent all statements within a Select-Case structure

Indent all statements within a loop structure

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Style Notes

Put at least a line of space between two methods

Put a comment line ‘-------------------- above a method

Put a comment describing the method above the method

Names of Const variables are put in all capital letters

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Flow Control II