ICS 021 Week 5

1
ICS 021 Week 5

• Week 5
• Control Arrays
• Debugging

2
Control Arrays

• Visual Basic provides us with arrays of standard
  data type and user defined types
• Dim inum(20) As Integer
• Dim studrec(100) As Studenttype
• Visual Basic also provides us with arrays of
  Controls
• We can create an array of Command buttons or
  List boxes, etc
• This enables efficient processing of the
  controls

3
Control Arrays 1

• Control Array is a number of controls that have
  the same event handler, the system passes the
  controls index into the procedure.

0 1 2
4
Control Arrays 2

• The Control Array event handler can use a select
  statement instead of an if statement.

0 1 2
5
Control Arrays Creating

• Three ways to create a control array
• Copy an existing control and paste it onto form
• Assign same name to more than one control
• Set Index property of a control to non-null value
• For each of the above Visual Basic will ask do
  you wish to create a control array

6

• Creating Control Arrays at run-time Load
  ControlName(Index) Unload ControlName(Index)
  
• Add more notes here

7
Demo 1 - control arrays

• Create a form with two text fields, a label to
  hold an answer and a control array of four
  command buttons.
• When a button is pressed the operation answer
  should be displayed in Label1 45 - 52 -7
  or 3 5 4

8
Select Case Statement Control Arrays

• Using the Select Case statement to choose which
  control within a control array has been
  pressedSub Command1_Click (Index As Integer)
  
• Dim result As Integer
• Select Case Index Case 0 call
  add(val(text1.text),val(text2.text),
• result) Case 1 etc
• End Selectlabel1.caption result
• End Sub

9
Demo 2 - Labels as a control array
Create array of Labels at design time
10
(No Transcript)
11
Dialog BoxesMessage Boxes 1

• Message Boxes are used when you want the user to
  choose from a limited number of options, or just
  to inform them of somethingConst
  MB_OKCANCEL 1Dim iResponse As
  IntegeriResponse MsgBox("Message",MB_OKCANCEL,"
  Title")
• They are used for warnings, confirmation, etc..

12
Message Boxes 2

• There are a standard range of button combinations
  and icons available MB_ICONSTOP MB_ICONQUESTION
  MB_ICONEXCLAMATION MB_ICONINFORMATION
• They can be added together to give the required
  Message BoxConst MB_OKCANCEL 1Const
  MB_ICONQUESTION 32Const MB_BOXSTYLE
  MB_ICONQUESTION MB_OKCANCELDim iResponse As
  IntegeriResponse MsgBox("Message",MB_BOXSTYLE,"
  Title")

13
Message Boxes 3

• You can act upon the users response to the
  message box Const MB_OKCANCEL 1 Const
  MB_ICONQUESTION 32 Const MB_BOXSTYLE
  MB_ICONQUESTION MB_OKCANCEL Const IDOK 1
  Dim iResponse As Integer show the message
  box iResponse MsgBox("Message",MB_BOXSTYLE,"Ti
  tle") check how the user exited If
  iResponse IDOK Then Label1.Caption You
  OKd Else Label1.Caption You Cancelled
  End If
• The message box can be application or system modal

14
Debugging - Introduction

• There are three types of errors
• Compile errors occur as a result of code that is
  incorrectly constructed including syntax error
• matched control structure, such as a Next
  statement without a corresponding For statement,
• or programming mistakes that violate the rules of
  Basic, such as a misspelled word, a missing
  separator,
• or a type mismatch.
• syntax errors include passing an incorrect number
  of arguments to an intrinsic function
• or forgetting to match parentheses

15
Source Of errors

• Run-time errors occur after the application
  starts to execute.
• attempting an illegal operation, such as writing
  to a file that doesn't exist
• or dividing by zero.
• Logical errors the program doesn't perform as
  intended, and produces incorrect results.

16
How to debug - overview

• Debugging is a process by which you find and
  resolve errors in your code.
• To debug code in Visual Basic,
• 1. Print the code, if you find it easier to read
  code on paper instead of onscreen.
• 2. Run the application to find trouble spots
• Run until an error stops execution,
• or halt execution manually when you suspect an
  error by choosing Break

17

• 3. Use debugging tools and techniques to isolate
  bugs and to monitor code flow
• Set breakpoints to halt execution at certain
  points to look for problems such as
• incorrect variable types,
• mixups in variable names,
• flaws in logical comparisons,
• endless loops,
• garbled output,
• problems with arrays, and so on.

18

• Add a watch expression at design time or while in
  break mode to allow you to monitor the value of a
  particular expression as your code runs.
• Single step or procedure step through your code
  to trace through the application as it's running.
• Use the Debug window to test individual lines of
  code or procedures, or to change values.
• Enter break mode and choose Calls from the Debug
  window to see where your code is currently
  executing and trace the path showing how it got
  there.

19

• 4. Try out bug fixes and then make edits
• Test individual lines of new or debugged code in
  the Debug window.
• Search and replace code for all occurrences of
  an error, checking other procedures, forms, or
  modules with related code.

20
Demo - debugging an application
21

• Students should ensure that they are familiar
  with the debugging techniques covered
• Faster development of software
• Examination questions

22
End of Lecture
Click House to Return to Main Menu