1. Visual Basic Programming
Making Decisions: Loops & Decision
Structures
©Copyright by Ronald P. Kessler, Ph.D.

2. Program Control: If…Then…Else Statement
Conditional statements allow us to make logical evaluations:
If Sales > 1200 then Commission= 0.08
BLOCK STYLE:
If Sales < 500 Then
Commission= .08
ElseIf Sales > 500 And Sales < 1000 Then
Commission= .10
Else
Commission = .25
End If
Nothing after Then
ElseIf is never alone
Optional: It “catches” “other” conditions
Must have End If for each If

3. If…Then…Else Statement Used to Make Logical Decision
If MessageBox.Show("Are you sure”,”Ron’s Store” , MessageBoxButtons.YesNo) = _ Windows.Forms.DialogResult.Yes Then
Me.Close()
Else
MessageBox.Show("Then make up your mind")
End If

4. “Nested” If…Then…Else
If txtPIN.Text = “123” Then
MsgBox "Congratulations, you remembered your myPIN”
btnOK.Enabled = True
If optReceipt.Checked = True Then
btnPrint.Enabled = True
Else
btnPrint.Enabled = False
End If
MsgBox “You dope. You can't even remember your myPIN. ”
txtPIN.Text = ""
txtPIN.Focus

5. Program Control: Select Case Statement
Select Case statements are used when we want to perform different actions for each value of a variable
Dim state as String = “”
Dim salesTax as Single = 0
Select Case state
Case “CA”
salesTax= .085
Case “AZ” , “NJ”
salesTax= .075
Case “NV”
salesTax= 0.3
Case Else
salesTax= 0
End Select
Variable to evaluate
Case can be value or string or condition
Optional: It “catches” “other” conditions
Must have End Select

6. Select Case Statement: Testing a Range of Values
Dim discount as Single = 0
Dim unitsOrdered as Integer = 0
Select Case unitsOrdered
Case 1 to 10
discount = 0
Case 11 to 19
discount = .05
Case Is >= 20
discount = .1
End Select

7. Using Loops...

8. For…Next Loop Statement Used to Add Numbers to a List Box
For…Next loops are called Counted loops
Dim x as Integer = 0 ‘loop control variable
For x = 1 To 100
lbNumbers.Items.Add(x)
Next x 1 2 3 4

9. Nested For…Next Loop Statement Used As a Counter...
Dim x as Integer = 0
Dim y as Integer = 0
For x = 1 To 3
For y = 1 To 5
lbNumbers.Items.Add(y)
Next y
Next x

10. For…Next Loop Statement Used As a Backwards Counter...
Dim x as Integer = 0
For x = 10 To 1 Step -1
ListBox1.Items.Add (x)
Next x

11. For…Next Loop Statement Used To Count by 2’s
Dim x as Integer = 0
For x = 2 To 20 Step 2
ListBox1.Items.Add (x)
Next x

12. For…Next Loop Statement Used To Count Backwards by 2’s
Dim x as Integer = 0
For x = 20 To 2 Step -2
ListBox1.Items.Add (x)
Next x

13. Do…While Statements (Conditional Loops)
Do While... Loop:
Dim myPIN as String =“”
Do While myPIN = “ ”
myPIN =InputBox(“Enter myPIN”)
Loop
Label1.Text = myPIN
Pre-test condition
Do ...While Loop:
Dim myPIN as String Do
myPIN = InputBox(“Enter myPIN”)
Loop While myPIN = “ ”
Label1.Text = myPIN
Post-test condition

14. Do Until Statements (Conditional Loops)
Do Until... Loop:
Dim myPIN as String =“”
Do Until myPIN = “Ron ”
myPIN =InputBox(“Enter myPIN”)
Loop
Label1.Text = myPIN
Do …Until Loop:
Dim myPIN as String = “” Do
myPIN = InputBox(“Enter myPIN”)
Loop Until myPIN = “Ron ” Or myPIN = “99”
Label1.Text = myPIN

15. Using Counts & Totals...

16. Counts vs Totals... Counts increase or decrease by a fixed amount...
Dim count as Integer = 0 Do
myPIN =InputBox(“Enter PIN”)
count = count +1
Loop Until myPIN = “9” or count =5
Label1.Text = count
Totals change by a variable amount…
Dim myPrice as Currency = 0
Dim myTotal as Currency = 0
Total = 0 Do
Price = InputBox(“Enter Price”)
myTotal = myTotal + myPrice
Loop Until myPrice = 0
Label1.Text = Total

17. Using the InputBox Function
InputBox is a “Built-In” VB function
ALL functions return a value
price = InputBox (“Please enter a price” , “Ron’s Store”)
Sub Form1_Load ()
Dim price as Decimal = 0 Do
price = InputBox (“Enter price of item...”)
Loop Until Price = 0
End Sub
InputBox returns Price as a Currency variable.
If they hit Cancel, then InputBox returns “” which will cause an error because “” is a string, not currency.

18. That’s All Folks!