1. Mark Dixon 1 15 – Structured Programming

2. Mark Dixon 2 Admin: Test 2 In class test –11 Feb 2014 –4 Feb 2014: revision (technique) session 50 mins short answer (1 - 15 lines) 10% of module mark

3. Mark Dixon 3 Questions: Functions Consider the following code: Function Smallest(num1, num2) If num1 < num2 Then Smallest = num1 Else Smallest = num2 End If End Function name a function. what is left in small after the following is executed? Dim small small = Smallest(23, 15) 15 Smallest

4. Mark Dixon 4 Session Aims & Objectives Aims –To highlight the fundamental ideas of the structured programming paradigm Objectives, by end of this week’s sessions, you should be able to: –create an abstract data type, which includes data, and routines –use this to reduce code length

5. Mark Dixon 5 Example: Ball Bounce v1 Ball Bounce Option Explicit Dim x Dim y Dim xInc Dim yInc Sub window_onLoad() window.setinterval "Main()", 20 xInc = 5 yInc = 3 End Sub Sub Main() x = imgBall.style.posLeft + xInc If x = document.body.clientWidth - imgBall.width Then xInc = -xInc Else imgBall.style.posLeft = x End If y = imgBall.style.posTop + yInc If y = document.body.clientHeight - imgBall.height Then yInc = -yInc Else imgBall.style.posTop = y End If End Sub

6. Mark Dixon 6 Structured Paradigm Program made up of –data structures (variables & arrays), and –routines (procedures & functions) that process the data within those structures. Each routine should perform a single, clearly identifiable operation. Each routine should be self-contained Abstract data type = structure + procedures

7. Mark Dixon 7 Self-Contained Routines Self-contained: –no references to external items (objects & variables) Function a1(h, f) a1 = (h + f) * f End Function Sub a2() imgBall.Style.posLeft = 0 End Sub yes no

8. Mark Dixon 8 Question: Self-contained Which of the following routines are self-contained? Dim s Function goo(h, f) goo = (h + f) * s End Function Function poo(j, k, vi) If j > 45 Then poo = k + vi Else poo = k - vi End If End Function no yes

9. Mark Dixon 9 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 u = Twice(4) Function Twice(a) Return a * 2 End Function Dim u As Long Dim a As Long a = 4 u = Twice() Function Twice() Return a * 2 End Function 

10. Mark Dixon 10 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) Half = num / 2 End Function 

11. Mark Dixon 11 Example: Ball Bounce v1 Ball Bounce Option Explicit Dim x Dim y Dim xInc Dim yInc Sub window_onLoad() window.setinterval "Main()", 20 xInc = 5 yInc = 3 End Sub Sub Main() x = imgBall.style.posLeft + xInc If x = document.body.clientWidth - imgBall.width Then xInc = -xInc Else imgBall.style.posLeft = x End If y = imgBall.style.posTop + yInc If y = document.body.clientHeight - imgBall.height Then yInc = -yInc Else imgBall.style.posTop = y End If End Sub

12. Mark Dixon 12 Example: Ball Bounce v2 Option Explicit Dim x Dim y Dim xInc Dim yInc Sub Init(tmpXInc, tmpYInc) xInc = tmpXInc yInc = tmpYInc End Sub Sub Move(img) x = img.style.posLeft + xInc If x = document.body.clientWidth - img.width Then xInc = -xInc Else img.style.posLeft = x End If y = img.style.posTop + yInc If y = document.body.clientHeight - img.height Then yInc = -yInc Else img.style.posTop = y End If End Sub Ball Bounce Option Explicit Sub window_onLoad() window.setinterval "Main()", 20 Init 5, 3 End Sub Sub Main() Move imgBall End Sub BallBounce.htm Sprite.vbs

13. Mark Dixon 13 Making a routine self-contained identify why it isn't self-contained: the call: Dim m Sub MoveMiddle() m = document.body.clientWidth / 2 picDog.style.posLeft = m End Sub MoveMiddle()

14. Mark Dixon 14 Making a routine self-contained if variables are only used by this routine, then make them local: the call: Sub MoveMiddle() Dim m m = document.body.clientWidth / 2 picDog.style.posLeft = m End Sub MoveMiddle()

15. Mark Dixon 15 Making a routine self-contained if variables / identifiers are used elsewhere, then use a parameter: the call now needs an actual parameter: Sub MoveMiddle(picAny) Dim m m = document.body.clientWidth / 2 picAny.style.posLeft = m End Sub MoveMiddle(picDog)

16. Mark Dixon 16 Making a routine self-contained some items are difficult to fix (e.g. document – built in object): the call: Sub MoveMiddle(picAny) Dim m m = document.body.clientWidth / 2 picAny.style.posLeft = m End Sub MoveMiddle(picDog) Either: - use parameter - leave it

17. Mark Dixon 17 Example: Balloon Shoot Question: –what objects? –what variables? –what procedures / functions?

18. Mark Dixon 18 Tutorial Exercise: Ball Bounce Learning Objective: To create and use your own class. Task 1: Get the Ball Bounce examples (1, 2, and 5) from the lecture working. Task 2: Add another sprite. Hint: Use Arrays. Task 3: Add another 5 sprites. Task 4: Add a hit method to the sprite class, which detects the collision with another sprite. Task 5: Modify your page to count the number of hits between the two sprites. Task 6: Modify your page to make sprites bounce off each other.

19. Mark Dixon 19 Tutorial Exercise: Balloon Shoot Learning Objective: To create and use your own classes. Task 1: Create the Balloon Shoot example (from the lecture) using object oriented concepts (classes, properties, methods, and instances) hint: use some of the code from your Interceptor example (from last week)