1. VB Core II Conditional statements Exception handling Loops Arrays Debugging

2. if statements If c > 5 Then x = 1 y = 3 End If If c > 5 Then x = 1: y = 3 If c > 5 Then x = 1 y = 3 Else z = 7 End If If c > 5 Then x = 1 y = 3 ElseIf c = 4 Then z = 7 Else x = 9 End If

3. Exercise – quadratic equation solver Create a form with – 3 textboxes to input values for a b and c (and labels as prompts) 2 labels where the roots will be shown A button captioned 'Solve' Code the button (square root function is sqr )

4. select Dim Number Number = 8 ' Initialize variable. Select Case Number ' Evaluate Number. Case 1 To 5 ' Number between 1 and 5, inclusive. x=4 Case 6, 7, 8 ' Number between 6 and 8. x=5 Case 9 To 10 ' Number is 9 or 10. x=6 Case Else ' Other values. x=7 End Select

5. Error and exception handling exception = problem event at run-time usually related to I/O eg file not found, server connection lost, invalid user input not a programming bug VB calls exception errors (Unlike Java) VB does not force exception handling

6. Error handlers – example - invalid numbers Private Sub Command1_Click() Dim num1 As Integer Dim num2 As Integer Dim result As Integer On Error GoTo myErrorHandler num1 = Text1.Text num2 = Text2.Text result = num1 + num2 Label1.Caption = result Exit Sub myErrorHandler: If Err.Number = 13 Then MsgBox ("Please enter a valid number") Else MsgBox (Err.Description) End If Resume Next End Sub Exercise Try this out in the calculator program Then deal with divide by zero (11)

7. For next loops Dim x as Integer, total As Integer total = 0 For x = 1 To 5 total = total + x Next Dim x as Integer, total As Integer total = 0 For x = 1 To 5 Step 2 total = total + x Next

8. Debugging – debug.print Debug.print x,y,z Immediate window – CTRL G Exercise – write a for next loop to add up the odd numbers from 1 to 9 inclusive. Use debug.print to check it works

9. Other loops Dim c As Integer c = 1 Do While c < 5 c = c + 1 Loop Dim c As Integer c = 1 Do Until c >4 c = c + 1 Loop Dim c As Integer c = 1 Do c = c + 1 Loop While c < 5 Dim c As Integer, x as integer c = 1 x=2 Do c = c + 1 Loop Until c>4 And x<>3

10. Arrays (fixed size) Dim x(100) As Integer Dim i As Integer For i = 0 To 100 x(i) = 99 Next Dim x(1 To 3, 1 To 3) As Integer Dim i as integer, j As Integer For i = 1 To 3 For j = 1 To 3 x(i, j) = 99 Next

11. Dynamic arrays Dim x() As Integer ReDim x(5) Dim i, j As Integer For i = 1 To 5 x(i) = 99 Next ReDim Preserve x(10) For i = 6 To 10 x(i) = 100 Next

12. Debugging

13. User defined type – record or struct Private Type employee payrollNumber As Integer name As String End Type Private Sub Command1_Click() Dim emp1 As employee emp1.name = "John" emp1.payrollNumber = 4082 End Sub Tidier Halfway to class Needed for Win32 API

14. Exercise Program a button so it finds the prime numbers up to 100 Produce output using Debug.print Use the Sieve of Eratosthenes: Mark off every second number after 2 Every third number after 3 Every fourth number after 4.. What is left are the primes