CSCI N331 VB .NET Programming
Lingma Acheson
Department of Computer and Information Science, IUPUI

Procedures
• procedure – a unit of code that executes when called from another place.
• Not a new face –
‘Sub procedure definition – a button click event
Private Sub btnDisplay_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnDisplay.Click
End Sub
Or: lstOutput.Items.
Clear() ‘sub procedure call
• procedure definition – Defines what to execute when the procedure is called.
• procedure call – Defines when to execute the procedure.
2

Procedures
• A procedure must have a name following by ().
E.g.
lstOutput.Items.
Clear() lstOutput.Items.
Add( “******” )
CDbl( txtInputOne.Text
)
• Purpose of using procedures – make your code wellorganized and easy to understand.
3

Without Using Procedures:
Button click event:
Create variables
Take two user inputs, and store them to variables
Perform the addition and display the result
Perform the subtraction and display the result
Perform the multiplication and display the result
Perform the division and display the result (handle divide by 0 situation here)
End of event
Procedures
Using Procedures:
Create variables
Button click event:
Take two user inputs, and store them to variables
Add()
Subtract()
Multiply()
Divide()
End of event
Define Add():
Perform the addition and display the result
Define Subtract():
Perform the subtraction and display the result
…
Define Divide()
Perform the division and display the result(handle divide by 0 situation here)

•
Sub Procedures
Sub procedure – execute a block of codes when called
• Define a Sub procedure:
Private Sub name ()
‘actions here
…
End Sub
• The key word
used by this Form.
means this Sub can only be
• The Sub procedure call must match with the Sub procedure definition.
5

Sub Procedures
• E.g. a user defined Sub definition and Sub call –
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnDisplay.Click
intFirst = CInt(nudFirst.Value) intSecond = CInt(nudSecond.Value)
Add() ‘Sub call. The program will look for a Sub definition with the same
‘name to decide what to do
End Sub
‘Sub definition
Private Sub Add()
Dim intResult As Integer = 0
‘intFirst and intSecond are global variables, so they can used by both Subs.
intResult= intFirst + intSecond txtAddResult.Text = CStr(intResult)
End Sub
…
6

– Purpose: for a specific procedure to use
– Scope: only used inside that procedure
– Where: created inside a procedure
– Purpose: a variable shared by different procedures
– Scope: the form, also called form variables, can be used anywhere in the same form
– Where: created at the beginning of the Class, outside of any procedures
7

Local Variables:
Add Button click event procedure:
‘3 local variables, only used
‘inside this procedure
Create variables 1, 2, and 3
Take user input and store in variable 1 and 2
Add variable 1 to variable 2 and store the result to variable 3
End of event procedure
Global Variables:
‘Create 2 global variables outside of any procedure, can be used anywhere
Create variables 1, 2
Add Button click event procedure:
Add()
End of event procedure
Procedure Add():
‘1 local variable, only used
‘inside this procedure
Create variable 3
‘use global variable 1 and 2
Take the user input and store in variable 1 and 2
‘use global variable 1 and 2, and
‘local variable 3
Add variable 1 to variable 2 and store the result to variable 3
End of Add procedure