CSC 162

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CSC 162

• Visual Basic I Programming

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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 ListBoxs 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.

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Procedures

• Event 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
  Functions name

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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

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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
  objects variable
• ByRef directly access the data in the calling
  objects variable, thus allowing it to be modified

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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 5
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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 25
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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()
• ' Local variables
• 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

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Homework

• Read Chapter 6.1 6.8

Lab Assignment
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.