1. Visual Basic I Programming
CSC 162
Visual Basic I Programming

2. ListBox Object Unlike a TextBox, a ListBox can hold multiple items.
Each item gets its own line.
Once the ListBox is full, it will automatically provide scroll bars to view all the contents.
A ListBox cannot be edited directly by the user.
A ListBox’s naming convention prefix is lst.
To add an item to a ListBox, use the .AddItem method:
lstNames.AddItem(strLastName & ", " & strFirstName)
Use the ListBox for outputting the Pythagorean Triples, since using Print runs the output off the form.

3. Procedures Event procedures Visual Basic procedures Sub procedures
respond to an event (mouse click, button press, etc.)
Visual Basic procedures
built-in procedures that perform common tasks (MsgBox, InputBox, etc.)
Sub procedures
programmer-defined procedures that perform tasks
Function procedures
programmer-defined procedures that perform “calculations” and return values through the Function’s name

4. Programmer-defined Procedures
May have a private or public scope.
Scope refers to the region in which the identifier can be referenced
An identifier with private scope may only be referenced from within the current module
An identifier with public scope may be referenced from anywhere within the current project

5. ByVal or ByRef
Procedures can be passed values (called parameters) from the calling object.
The parameter can either be passed by value (ByVal) or by reference (ByRef).
ByVal makes a copy of the value being passed, thus preserving the original value in the calling object’s variable
ByRef directly access the data in the calling object’s variable, thus allowing it to be modified

6. Sub Procedure Example (ByVal)
Private Sub PrintSquare(ByVal intNum As Integer)
intNum = intNum ^ 2
Print intNum
End Sub
Private Sub cmdPrint_Click()
' Local variables
Dim intValue As Integer
' Get User Data
intValue = Val(txtNumber.Text)
' Print Initial Value
Print intValue
' Call to Sub Procedure
Call PrintSquare(intValue)
' Print Final Value
Output: (Given 5 in txtNumber) 5 25

7. Sub Procedure Example (ByRef)
Private Sub PrintSquare(ByRef intNum As Integer)
intNum = intNum ^ 2
Print intNum
End Sub
Private Sub cmdPrint_Click()
' Local variables
Dim intValue As Integer
' Get User Data
intValue = Val(txtNumber.Text)
' Print Initial Value
Print intValue
' Call to Sub Procedure
Call PrintSquare(intValue)
' Print Final Value
Output: (Given 5 in txtNumber) 5 25

8. Function Procedure Example
Private Function Area(ByVal intLength As Integer, ByVal intWidth As Integer) As Integer
' Local variables
Dim intA As Integer ' Local variable for the Area
intA = intLength * intWidth
Area = intA ' Return final value
End Function
Private Sub cmdFindArea_Click()
Dim intL As Integer ' User's entered length
Dim intW As Integer ' User's entered width
' Get User Data
intL = Val(txtLength.Text)
intW = Val(txtWidthr.Text)
' Print Area
Print Area(intL, intW)
End Sub

9. Homework Lab Assignment Read Chapter 6.1 – 6.8
Read in two legs of a right triangle from the user in TextBoxes. Compute the hypotenuse using the Pythagorean Theorem. Return the value in a Label. To compute the hypotenuse, create a function called Pythag that takes two Singles as input and returns its answer as a Single.