More Visual Basic
Code: if-then-else, for loops
Controls: Multiple forms, List
Boxes, Radio buttons, frames,
Data Type
At the lowest level, all data stored in the
computers is written in 1’s and 0’s (binary)
How that data gets interpreted, what actions
can be performed on it, etc. depends in part
on the “data type” associated with it
We let the computer know how we mean to
interpret a variable by declaring its type, e.g.
Dim Count As Integer
‘ (Option Explicit makes VB strongly typed)
Some VB types
integer : a whole number, that is a number
with no fractional part.
single: A number with a decimal point, such
as 3.14159 (called a “float” in C)
double: A number with a decimal point, such
as 3.14159265358 (called a “float” in C); is
more precise than a single; it also allows for a
greater range of numbers
More VB Types
String: words or text, that is, groups of
letters, numbers and symbols
Boolean: a variable that can only be true or
false (real type as opposed to C’s)
Currency: data type used to represent
money (dollars and cents); only two decimal
places are shown; takes care of unusual
rounding associated with money
(pp. 26-30 in VB & VBA)
The Control type
When you drag a control onto a form,
you don’t need to declare it
Reserving memory locations and so on is
done automatically
However, if you need to remember a
control (e.g. to keep track of what
button you pressed), you declare a
control
Command Type Demo
The Control Type (cont.)
Dim ControlTrack As Control
Private Sub cmdButton1_Click()
Set ControlTrack = cmdButton1
End Sub
Private Sub cmdButton2_Click()
Set ControlTrack = cmdButton2
End Sub
Private Sub cmdButton3_Click()
Text1.Text = "you last pressed " + ControlTrack.Caption
End Sub
Binding
You will notice a difference between typing
“cmdButton1.” and typing “ControlTrack.”
In the first case, VB knows that it is a
CommandButton control and so provides the
properties in a drop-down list (an example of
early binding)
In the second case, VB does not know the
type of control that ControlTrack is until the
program runs, hence, it cannot provide the
properties (an example of late binding)
If-Then
Tests a condition and executes
statements within the body (block) of
the if structure provided the condition
was true and skips over those steps
otherwise
(pp.366-370 VB & VBA)
If-Then Example
If State=“PA” Then
Price=Price*(1.06)
End If ‘State
‘Recalculates the price factoring in the PA
‘sales tax if the state is PA
‘Note strings are more easily compared in VB
Condition
A condition is an expression that evaluates to
a Boolean value (true or false)
It often involves a comparison
A>B
A >= B
A<B
A <= B
A=B
A <> B
(is A greater than B?)
(is A greater than or equal to B?)
(is A less than B?)
(is A less than or equal to B?)
(is A equal to B?)
(is A not equal to B?)
‘(does not use !)
Compound Conditions
Boolean operators can be used to combine
conditions
And: both expressions must evaluate to
true for combination to be true
Or:
if either expression evaluates to true,
the combination is true
Not: if an expression evaluates to true,
Not(expression) evaluates to false and vice
versa
If-Then-Else
The If-Then-Else structure provides two
statement blocks, one to execute if the
condition is true, the other to execute if
the condition is false
If-Then-Else Example
If State=“PA” Then
If City = “Phila” Then
Price=Price*(1.07)
Else
Price=Price*(1.06)
End If ‘City
End If ‘State
‘This is also an example of nested if’s (an if within an if)
ElseIf
If Grade > 94 Then
Letter_Grade = “A”
ElseIf Grade > 86 Then
Letter_Grade = “B”
ElseIf Grade > 78 Then
Letter_Grade = “C”
ElseIf Grade > 70 Then
Letter_Grade=“D”
Else
Letter_Grade=“F”
EndIf
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 fornext 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
For-Next Example
(pp. 320-322 in VB & VBA)
For i=1 To Num_Years
Principle=Principle*(1+ Interest/100)
Next I
‘Calculates Interest (compounded yearly) on Principle
‘over Num_Years
Multiple Forms
A project can consist of a few forms
Typically one form (the start-up form)
appears first
Events associated with it bring up the
other forms
One can have multiple forms showing,
or one can hide all but the one the user
is interfacing with
Message Box
A special case of multiple form is a
message box, a little window with a
warning popping up
Message Box function (pp. 429-432 in VB
& VBA)
Dim r As Integer
Private Sub Command1_Click()
r = MsgBox("Body Message", vbOKOnly, "Caption Message")
End Sub
Form Events
To control various forms we want to
understand their methods and events
Initialize: occurs when form is first
referenced, occurs once unless form is
“terminated”
Load: occurs when the specific properties
of the form are put into memory, occurs
once unless form is “unloaded”
More Form Events
Resize: occurs when the form is moved or
its size is altered
There’s a Resize called by load
Activate: occurs when a user switches
forms
The events occur in the order given above
Initialize  Load  Resize  Activate
Form methods
Show: displays (makes visible) a form
This will include the loading a form if the form
was not loaded previously
Hide: makes a form invisible
(pp. 37-43 in Visual Basic Controls)
Adding another form
Go to Project/Add Form
Choose whether you want to make a New
form or include an already Existing form
An existing form is not copied and brought
into the project folder, you must choose to do
that (right click on the form in the upper right
hand side of the IDE and choose Save
frmWhatever As …
Scope
Procedure-level: variable is available only
with subroutine or function in which it is
declared (local)
Module-level: variable is available to all
subroutines within a module, e.g. all the
subroutines associated with a form
Friend: variable is available to other forms
within a project, but is not available to
anyone outside the project
Public: variable is available to other projects
Multi-Form Demo
Form 1 Code
Public FirstName As String
Private Sub cmdShowForm2_Click()
FirstName = txtForm1.Text
frmForm2.Show
frmForm1.Hide
End Sub
Form 2 Code
Private Sub cmdReturn_Click()
frmForm2.Hide
frmForm1.Show
End Sub
Private Sub Form_Activate()
txtForm2.Text = frmForm1.FirstName
End Sub
ListBox
Some ListBox Properties and
Methods
MultiSelect: allows more than one item to
be selected
1-Simple
SelCount: gives the number of highlighted
items
Text: the text of the currently highlighted
item
AddItem: adds a string to the list
(pp. 182-186 in Visual Basic Controls)
Some ListBox Code
Private Sub Form_Load()
lstCourse.AddItem ("csc 362")
End Sub
Private Sub lstCourse_Click()
If lstCourse.SelCount = 1 Then
txtCourse1.Text = lstCourse.Text
End If
If lstCourse.SelCount = 2 Then
txtCourse2.Text = lstCourse.Text
End If
End Sub
Radio Buttons
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)
(pp. 292-296 Visual Basic Controls)
Frames in action
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
Some Frame Code
(pp. 142-143 Visual Basic Controls)
Private Sub cmdCommand1_Click()
fraFrame1.Enabled = False
End Sub
‘Disables everything contained in Frame1