1. 17 – Modular Design in ASP

2. Questions: Session variables
Write a line of VB code to put 74 into a session variable called score.
Write VB code that adds 1 to a variable called g, when a session variable called i is over 25.
Session("a") = 74
If Session("i") > 25 Then
g = g + 1
End If

3. Session Aims & Objectives
Highlight modular design techniques, and demonstrate them in ASP
Objectives, by end of this week’s sessions, you should be able to:
Identify dependencies between lines of code
Determine whether a routine is self-contained
Use procedures, functions, parameters, and modules (shared VB script files) in ASP

4. Example: Apples (analysis)
SPECIFICATION
User Requirements
help young children learn to count from 1 to 10
Software Requirements
Functional:
computer selects number between 1 and 10
computer displays that number of apples
user types digits
computer compares digits to number of apples
Non-functional should be easy to use and interesting

5. Example: Apples v2 (design)
Functionality:
computer selects number between 1 and 10
computer displays that number of apples
user types digits
computer compares digits to number of apples    

6. Example: Apples v2 (code)
Apples.aspx
Dim n As Long
Sub Page_Load()
Dim html As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
quest.InnerHtml = html
Session("NumApples") = n
msg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
Dim n As Long
Sub Page_Load()
Dim html As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
quest.InnerHtml = html
Session("NumApples") = n
msg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
If CInt(txtAns.Value) = CInt(n) Then
msg.InnerHtml = "Correct, well done!"
Else
msg.InnerHtml = "Sorry, please try again."
End If
btnStart.Disabled = False
btnCheck.Disabled = True
End Sub

7. Example: Apples v2 (code)
Apples.aspx
Dim n As Long
Sub Page_Load()
Dim html As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
quest.InnerHtml = html
Session("NumApples") = n
msg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
If CInt(txtAns.Value) = CInt(n) Then
msg.InnerHtml = "Correct, well done!"
Else
msg.InnerHtml = "Sorry, please try again."
End If
btnStart.Disabled = False
btnCheck.Disabled = True
End Sub
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
If CInt(txtAns.Value) = CInt(n) Then
msg.InnerHtml = "Correct, well done!"
Else
msg.InnerHtml = "Sorry, please try again."
End If
btnStart.Disabled = False
btnCheck.Disabled = True
End Sub

8. Problem Solving Strategies
bottom-up
Create a detailed solution first
Then look for best solution
refactoring – process of:
changing internal design of code,
without altering what it does
top-down
plan overall design
fill in details
in practice mixed – novices favour bot-up, experts top-down

9. Dry Running Useful to understand code: Dim a As Long Dim b As Long
Dim c As Double
a = 12
b = a + 5
c = b a b c - - - - - - - - - 12 - - 12 17 - 12 17
18.25

10. Dependencies: Numeric Variables
consider the following code: 1 Dim h As Long 2 Dim q As Long h = q = h + 2
line 3 is dependent on line 1 (it involves h, it needs line 1)
line 4 is dependent on line 3 and line 2

11. Dependencies: String Variables
consider the following code: 1 Dim surname As String 2 Dim forename As String 3 Dim initials As String surname = "Jones" forename = "Alice" initials = Left(surname, 1) & Left(forename, 1)
line 6 is dependent on lines 4 and 5 (it uses the values in the surname and forename variables)
line 5 is dependent on line 2
line 4 is dependent on line 1

12. Question: Variable Dependencies
What dependencies exist in the following code?
Dim q1 As String
Dim q2 As String
Dim u As Long
Dim o As Long
Dim g As Long
q1 = "It is not enough to have a good mind."
q2 = "The main thing is to use it well."
u = Len(q1)
o = Len(q2)
g = u + o

13. Example: Apples (Dependencies)
Dim n As Long
Sub Page_Load()
Dim html As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
quest.InnerHtml = html
Session("NumApples") = n
msg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
Difficult to see dependencies for lines far apart

14. Example: Apples (Dependencies)
Dim n As Long
Sub Page_Load()
Dim html As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
Session("NumApples") = n
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
quest.InnerHtml = html
msg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
Put dependent lines close together

15. Example: Apples v3 (design)
Functionality:
computer selects number between 1 and 10
computer displays that number of apples
user types digits
computer compares digits to number of apples and displays number of apples typed by user

16. Example: Apples v3 (code)
Apples.aspx
copy + paste
Dim n As Long
Sub Page_Load()
Dim html As String
Dim msg As String
Dim a As Long
If Request.Form("btnStart") > "" Then
n = 1 + Int(Rnd() * 9)
Session("NumApples") = n
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
parQuest.InnerHtml = html
parMsg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
msg = ""
For a = 1 To txtAns.Value
msg = msg & "<img src=Apple.gif>"
If CInt(txtAns.Value) = CInt(n) Then
msg = msg & "Correct, well done!"
Else
msg = msg & "Sorry, please try again."
End If
parMsg.InnerHtml = msg
btnStart.Disabled = False
btnCheck.Disabled = True
End Sub
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
msg = ""
For a = 1 To txtAns.Value
msg = msg & "<img src=Apple.gif>"
Next
If CInt(txtAns.Value) = CInt(n) Then
msg = msg & "Correct, well done!"
Else
msg = msg & "Sorry, please try again."
End If
parMsg.InnerHtml = msg
btnStart.Disabled = False
btnCheck.Disabled = True
End Sub

17. Modular Design What do lines do (group summary)?
n = 1 + Int(Rnd() * 9)
Session("NumApples") = n
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
parQuest.InnerHtml = html
parMsg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
Pick Num. of Apples
Display Question
Prepare for Response

18. Modular Design (top level)
Top level reads like English algorithm:
Dim n As Long
Dim html As String
Dim msg As String
Dim a As Long
Sub Page_Load()
If Request.Form("btnStart") > "" Then
PickRandomNumberOfApples
DisplayApplesQuest
PrepareForResponse
ElseIf Request.Form("btnCheck") > "" Then
n = Session("NumApples")
DisplayApplesUser
DisplayFeedback
PrepareForQuest
End If
End Sub

19. Modular Design (detail)
Procedures contain (hide) detail:
Sub PickRandomNumberOfApples()
n = 1 + Int(Rnd() * 9)
Session("NumApples") = n
End Sub
Sub DisplayApplesQuest()
Dim html As String
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
parQuest.InnerHtml = html
Sub DisplayApplesUser()
msg = ""
For a = 1 To txtAns.Value
msg = msg & "<img src=Apple.gif>"
Sub DisplayFeedback()
If CInt(txtAns.Value) = CInt(n) Then
msg = msg & "Correct, well done!"
Else
msg = msg & "Sorry, please try again."
End If
parMsg.InnerHtml = msg
Sub PrepareForResponse()
parMsg.InnerHtml = ""
txtAns.Value = ""
btnStart.Disabled = True
btnCheck.Disabled = False
Sub PrepareForQuest()
btnStart.Disabled = False
btnCheck.Disabled = True
Sub DisplayApplesQuest()
html = "How many apples are there?<br />"
For a = 1 To n
html = html & "<img src=Apple.gif>"
Next
parQuest.InnerHtml = html
End Sub
Sub DisplayApplesUser()
msg = ""
For a = 1 To txtAns.Value
msg = msg & "<img src=Apple.gif>"

20. Routines: Self-Contained
Good design principle:
routines (functions and procedures) should be self-contained (easier to re-use in other programs)
Dim u As Long
Dim a As Long
a = 4
u = Twice()
Function Twice()
Return a * 2
End Function
Dim u As Long
u = Twice(4)
Function Twice(a As Long)
Return a * 2
End Function  

21. Question: Self-Contained Routines
Are the following routines self contained?
Dim num1
Dim num2
Dim diff
Sub Compare()
diff = num1 - num2
End Sub
Function Half(num As Double) As Double
Return num / 2
End Function  

22. Debugging key skill: first step typical pattern in early tutorials:
locate the cause of a bug
using testing methods
first step
narrow it down as much as possible
typical pattern in early tutorials:
student: it doesn't work
lecturer: what doesn't work
student: my code
lecturer: yes, but which bit exactly
student: ????
lecturer: run your program, take me through it, which bits work, and where exactly does it go wrong
student: when I click this, nothing happens
lecturer: which bit of code is responsible for doing that?
student: this bit

23. Problem Solving: 9 dots
Join all 9 dots
with straight continuous lines

24. Problem Solving Process (Name Split)
Problem: a variable exists called n. This contains a person's full name (forename, then surname ). It needs to be split into two separate variables.
Dim n As String
n = "Ruth Jones"
Solution Process:
What do I do to solve this manually (on paper)?
How do I know where the forename ends and the surname begins?
The space is the key:
Find the space
everything before the space is the forename
everything after the space is the surname

25. Tutorial Exercise: Apples
LEARNING OBJECTIVE: identify dependencies between lines of code refactor code: dependent lines closer refactor code: split into routines (procedures and functions) refactor code: make routines self-contained
Task 1: Get the Apples v3 example (from the lecture) working
Task 2: Modify your page to keep a score. HINT: Try to identify the routines first, then fill in the code.