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11 – Parameters

11 – Parameters. Question: Arrays. How many array variables are in the following code: Dim x Dim y Dim f(4) x = 12 y = 6 f(2) = 21. 1. Question: Arrays. How many errors are in the following code: Dim x Dim y Dim f(4) f = 3 y(3) = 6 f(1) = 19 f(5) = 21. Session Aims & Objectives.

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11 – Parameters

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  1. 11 – Parameters

  2. Question: Arrays • How many array variables are in the following code:Dim xDim yDim f(4) x = 12 y = 6 f(2) = 21 1

  3. Question: Arrays • How many errors are in the following code:Dim xDim yDim f(4) f = 3 y(3) = 6 f(1) = 19 f(5) = 21

  4. Session Aims & Objectives • Aims • To introducepassing parameters/arguments to procedures to make them more general purpose • Objectives, after this week’s sessions, you should be able to: • use parameters in your programs to make procedures more flexible • distinguish between formal and actual parameters • pass parameters by reference and by value • identify and correct parameter errors

  5. Example: Clock (analysis) • SPECIFICATION • User Requirements • to know what the time is • Software Requirements • Functional: • display current time in analogue (traditional clock face) format • Non-functionalshould be easy to read

  6. Example: Clock (user interface) • 14 objects: • 12 numbers • mid point • second point (moving)

  7. Example: Clock v0 (HTML) <html> <head><title></title></head> <body> <div id=div1 style="position: absolute;">1</div> <div id=div2 style="position: absolute;">2</div> <div id=div3 style="position: absolute;">3</div> <div id=div4 style="position: absolute;">4</div> <div id=div5 style="position: absolute;">5</div> <div id=div6 style="position: absolute;">6</div> <div id=div7 style="position: absolute;">7</div> <div id=div8 style="position: absolute;">8</div> <div id=div9 style="position: absolute;">9</div> <div id=div10 style="position: absolute;">10</div> <div id=div11 style="position: absolute;">11</div> <div id=div12 style="position: absolute;">12</div> <img id=imgMid style="position: absolute;" src="dot.gif" /> <img id=imgSec style="position: absolute;" src="dot.gif" /> </body> </html>

  8. Example: Clock v1 (HTML) • Remove 'hard coded' tags <html> <head><title></title></head> <body> <img id=imgMid style="position: absolute;" src="dot.gif" /> <img id=imgSec style="position: absolute;" src="dot.gif" /> </body> </html>

  9. Example: Clock v1 (code) • use loop to put in tags Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style='position: absolute;'>" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 … … … div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setInterval "ShowHands", 500 End Sub

  10. Example: Clock v1 (code) Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub current time and date Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub

  11. Example: Clock v1 (code) Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 … … … div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub

  12. Example: Clock v1 (code) • same 2 lines duplicated • not identical • different object • different angle Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub

  13. Problem: Inflexible Procedure • Procedure does exactly the same each time Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) Position End Sub Sub Position() imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub

  14. Parameters/Arguments: What Milk Make cup of tea Sugars • Sometimes procedures need information • Making a cup of tea: • milk, and number of sugars • Makes them more flexible

  15. Parameters: How • Procedure Declaration • formal parameters define name • Procedure Call • actual parameters list values in order Option Explicit Dim res Sub Calc(Num1, Num2) res = Num1 * Num2 End Sub Sub btnCalc_Click() Calc 5, 2 Calc 11, 15 End Sub

  16. Parameters: How

  17. Error: Wrong number of arguments Option Explicit Sub Twice(num) parResult.innerText = num * 2 End Sub Twice 3 Twice 4, 3 Twice

  18. Questions: Parameters • Name the procedures in the following code and state how many parameters they take: Sub hello(s, x) Dim i s = "" For i = 1 To x s = s + "Hello" Next End Sub Sub DisplayScore() parScore.innerText = score End Sub hello takes 2 parameters DisplayScore takes 0 parameters

  19. Questions: Parameters Given the following declaration: • What will the following put in parRes? Sub thing(Num1, Num2, Num3) Dim tmpOutput tmpOutput = (Num1 + Num2) * Num3 parRes.innerText = tmpOutput End Sub thing 2, 3, 6 thing 6, 3, 2 thing 20, 5, 2 30 18 50

  20. Example: Clock v2 (code) Position div1, ang Position div2, ang * 2 Position div3, ang * 3 Position div4, ang * 4 … … … Position div9, ang * 9 Position div10, ang * 10 Position div11, ang * 11 Position div12, ang * 12 Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 Position div1, ang Position div2, ang * 2 Position div3, ang * 3 Position div4, ang * 4 Position div5, ang * 5 Position div6, ang * 6 Position div7, ang * 7 Position div8, ang * 8 Position div9, ang * 9 Position div10, ang * 10 Position div11, ang * 11 Position div12, ang * 12 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) Position imgSec, ang * s End Sub Sub Position(objO, a) objO.style.pixelleft = imgMid.style.pixelleft + Sin(a) * 200 objO.style.pixeltop = imgMid.style.pixeltop - Cos(a) * 200 End Sub Position imgSec, ang * s Sub Position(objO, a) objO.style.pixelleft = imgMid.style.pixelleft + Sin(a) * 200 objO.style.pixeltop = imgMid.style.pixeltop - Cos(a) * 200 End Sub

  21. Comparison of Clock Code v0 (64 lines) v1 (59 lines) v2 (51 lines) (2474 bytes) (2064 bytes) (941 bytes) <html> <head><title></title></head> <body> <div id=div1 style="position: absolute;">1</div> <div id=div2 style="position: absolute;">2</div> <div id=div3 style="position: absolute;">3</div> <div id=div4 style="position: absolute;">4</div> <div id=div5 style="position: absolute;">5</div> <div id=div6 style="position: absolute;">6</div> <div id=div7 style="position: absolute;">7</div> <div id=div8 style="position: absolute;">8</div> <div id=div9 style="position: absolute;">9</div> <div id=div10 style="position: absolute;">10</div> <div id=div11 style="position: absolute;">11</div> <div id=div12 style="position: absolute;">12</div> <img id=imgMid style="position: absolute;" src=dot.gif /> <img id=imgSec style="position: absolute;" src=dot.gif /> </body> </html> <script language=VBScript> Option Explicit Sub window_OnLoad() Dim ang imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub </script> <html> <head><title></title></head> <body> <img id=imgMid style="position: absolute;" src=dot.gif /> <img id=imgSec style="position: absolute;" src=dot.gif /> </body> </html> <script language=VBScript> Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 div1.style.pixelleft = imgMid.style.pixelleft + Sin(ang) * 200 div1.style.pixeltop = imgMid.style.pixeltop - Cos(ang) * 200 div2.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 2) * 200 div2.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 2) * 200 div3.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 3) * 200 div3.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 3) * 200 div4.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 4) * 200 div4.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 4) * 200 div5.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 5) * 200 div5.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 5) * 200 div6.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 6) * 200 div6.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 6) * 200 div7.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 7) * 200 div7.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 7) * 200 div8.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 8) * 200 div8.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 8) * 200 div9.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 9) * 200 div9.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 9) * 200 div10.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 10) * 200 div10.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 10) * 200 div11.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 11) * 200 div11.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 11) * 200 div12.style.pixelleft = imgMid.style.pixelleft + Sin(ang * 12) * 200 div12.style.pixeltop = imgMid.style.pixeltop - Cos(ang * 12) * 200 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) imgSec.style.pixelleft = imgMid.style.pixelleft + Sin(ang * s) * 200 imgSec.style.pixeltop = imgMid.style.pixeltop - Cos(ang * s) * 200 End Sub </script> <html> <head><title></title></head> <body> <img id=imgMid style="position: absolute;" src=dot.gif /> <img id=imgSec style="position: absolute;" src=dot.gif /> </body> </html> <script language=VBScript> Option Explicit Sub window_OnLoad() Dim ang Dim s Dim i s = "" For i = 1 To 12 s = s & "<div id=div" & i & " style=""position: absolute;"">" & i & "</div>" Next document.body.innerHTML = s & document.body.innerHTML imgMid.style.pixelleft = document.body.clientwidth / 2 imgMid.style.pixeltop = document.body.clientheight / 2 ang = 6.2 / 12 Position div1, ang Position div2, ang * 2 Position div3, ang * 3 Position div4, ang * 4 Position div5, ang * 5 Position div6, ang * 6 Position div7, ang * 7 Position div8, ang * 8 Position div9, ang * 9 Position div10, ang * 10 Position div11, ang * 11 Position div12, ang * 12 window.setinterval "ShowHands", 500 End Sub Sub ShowHands() Dim ang Dim s ang = 6.2 / 60 s = Second(Now()) Position imgSec, ang * s End Sub Sub Position(objO, a) objO.style.pixelleft = imgMid.style.pixelleft + Sin(a) * 200 objO.style.pixeltop = imgMid.style.pixeltop - Cos(a) * 200 End Sub </script>

  22. Example: Clock v3 • Use for loop instead of repeated calls Position div1, ang Position div2, ang * 2 Position div3, ang * 3 Position div4, ang * 4 Position div5, ang * 5 Position div6, ang * 6 Position div7, ang * 7 Position div8, ang * 8 Position div9, ang * 9 Position div10, ang * 10 Position div11, ang * 11 Position div12, ang * 12 For i = 1 To 12 Position document.getElementById("div" & i), ang * i Next

  23. Example: Clock v4

  24. Memory Addresses • Memory addresses - keep track of where variables are stored in memory • Every byte (position) in memory has a memory address: • e.g. variable identified by name xstored at location 63542(address of the first byte of data for variable x) Computer Memory 0 63542 x 23 Identifier Value

  25. Example: Change the Value

  26. Parameter Passing Methods • 2 ways to pass parameters to procedures: • Passing by Value: literalvalue is passed from the call to the definitionSub Change1(ByVal x) …End Sub • Passing by Reference: variable’s memory address (a reference to the variables position in memory) is passed from the call to the definitionSub Change2(ByRef y) …End Sub

  27. Why pass by reference? Change Set ByVal x ByRef x • Previously, used parameters to pass data into a procedure (input) • Pass by reference, allows: • the procedure to change the value of the passed variable • data to be input and output via parameters

  28. What can be passed • Pass by value – both literals and variables can be passed (variables are substituted by their value)Change1 y Change1 21  • Pass by reference – only variables can be passed (in fact the variable’s memory address is passed)Change2 y literals cannot be passed – they have no memory address Change2 21  ERROR

  29. Two results? integer (total) TotAve double (average) • Total and Average algorithms share a lot of code • Useful to combine them • TotAve procedure:

  30. Example: Total and Average Sub TotAve(ByRef T, ByRef A) Dim i T = 0 For i = 1 to 5 T = T + Nums(i) Next A = T / 5 End Sub tot = 0 ave = 0 TotAve tot, ave ' What is the value of ave and tot? var T TotAve var A

  31. Questions: Parameter Passing • Consider the following code: Dim a Sub Add(ByRef item, ByVal extra) item = item + extra End Sub a = 5 • What is the value of a, after each of these: Add a, 3 Add a, a Add 4, 4 8 16 Error – cannot pass 4 by reference

  32. Tutorial Exercise: Clock • LEARNING OBJECTIVE: • use parameters provided by event procedures • Task 1: Get the Clock (v2) example (from the lecture) working. • Task 2: Modify your code – display lots of dots for the second hand (as per v3). • Task 3: Modify your code – add an hour and minute hand

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