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07 – Iterative Execution

07 – Iterative Execution. Session Aims & Objectives. Aims To introduce the main concepts involved in getting the machine to perform repetitive tasks. Objectives, by end of this week’s sessions, you should be able to: identify and correct errors in For loops

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07 – Iterative Execution

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  1. 07 – Iterative Execution

  2. Session Aims & Objectives • Aims • To introduce the main concepts involved in getting the machine to perform repetitive tasks. • Objectives,by end of this week’s sessions, you should be able to: • identify and correct errors in For loops • create a For loop to repeat code a known number of times • identify and correct errors in Do loops • create a Do loop to repeat code an unknown number of times

  3. Example: Hello v0 • 1 user click: 1 Hello (1 line of code) <html> <head><title>Hello</title></head> <body> <input id="btnHello" type="button" value="Hello" /> <p id="parHello"></p> </body> </html> <script language="vbscript"> Option Explicit Sub btnHello_OnClick() parHello.innerHTML = parHello.innerHTML & "Hello<br>" End Sub </script>

  4. Example: Hello v1 • 1 user click: 10 Hellos (10 lines of code) Lots of lines imagine 300 Hellos <script language="vbscript"> Option Explicit Sub btnHello_OnClick() parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" End Sub </script>

  5. Example: Hello v2 • 1 user click: 10 Hellos (4 lines of code) <script language="vbscript"> Option Explicit Sub btnHello_OnClick() Dim h For h = 1 To 10 parHello.innerHTML = parHello.innerHTML & "Hello<br>" Next End Sub </script>

  6. For ... Next statement • repeat code known number of times • reduces length of code • easier to change • Syntax:Forvariable=startToendstatementblockNext

  7. Advantages • Less code: • This makes program: • Easier to read • Easier to change (imagine 500 Hellos) Hello v1 Hello v2 Option Explicit Sub btnGo_OnClick() parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" parHello.innerHTML = parHello.innerHTML & "Hello<br>" End Sub Option Explicit Sub btnGo_OnClick() Dim h For h = 1 To 10 parHello.innerHTML = parHello.innerHTML & "Hello<br>" Next End Sub 10lines 4 lines

  8. Example: Pendulum v1 <html> <head><title>Pendulum</title></head> <body style="margin: 0;"> <img id="imgMid" src="Dot.gif" style="position: absolute;" /> <img id="imgPend" src="Pend.gif" style="position: absolute;" /> </body> </html> <script language="vbscript"> Option Explicit Dim ang Dim speed Sub window_onload() imgMid.style.pixelLeft = document.body.clientWidth / 2 imgMid.style.pixelTop = document.body.clientHeight / 3 window.setInterval "Swing()", 25 ang = 0 speed = 0.04 End Sub Sub Swing() ang = ang + speed If ang > 0.5 Or ang < -0.5 Then speed = -speed End If imgPend.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 150 imgPend.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 150 End Sub </script>

  9. Example: Pendulum v2 <body style="margin: 0;"> <img id="imgMid" src="Dot.gif" style="position: absolute;" /> <img id="imgArm1" src="Dot.gif" style="position: absolute;" /> <img id="imgArm2" src="Dot.gif" style="position: absolute;" /> <img id="imgArm3" src="Dot.gif" style="position: absolute;" /> <img id="imgArm4" src="Dot.gif" style="position: absolute;" /> <img id="imgArm5" src="Dot.gif" style="position: absolute;" /> <img id="imgArm6" src="Dot.gif" style="position: absolute;" /> <img id="imgArm7" src="Dot.gif" style="position: absolute;" /> <img id="imgArm8" src="Dot.gif" style="position: absolute;" /> <img id="imgArm9" src="Dot.gif" style="position: absolute;" /> <img id="imgPend" src="Pend.gif" style="position: absolute;" /> </body> … Sub Swing() ang = ang + speed If ang > 0.5 Or ang < -0.5 Then speed = -speed End If imgPend.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 150 imgPend.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 150 imgArm1.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 15 imgArm1.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 15 imgArm2.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 30 imgArm2.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 30 imgArm3.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 45 imgArm3.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 45 imgArm4.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 60 imgArm4.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 60 imgArm5.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 75 imgArm5.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 75 imgArm6.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 90 imgArm6.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 90 imgArm7.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 105 imgArm7.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 105 imgArm8.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 120 imgArm8.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 120 imgArm9.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 135 imgArm9.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 135 End Sub </script> 56 lines of code

  10. Example: Pendulum v3 <body style="margin: 0;"> <img id="imgMid" src="Dot.gif" style="position: absolute;" /> <img id="imgArm1" src="Dot.gif" style="position: absolute;" /> <img id="imgArm2" src="Dot.gif" style="position: absolute;" /> <img id="imgArm3" src="Dot.gif" style="position: absolute;" /> <img id="imgArm4" src="Dot.gif" style="position: absolute;" /> <img id="imgArm5" src="Dot.gif" style="position: absolute;" /> <img id="imgArm6" src="Dot.gif" style="position: absolute;" /> <img id="imgArm7" src="Dot.gif" style="position: absolute;" /> <img id="imgArm8" src="Dot.gif" style="position: absolute;" /> <img id="imgArm9" src="Dot.gif" style="position: absolute;" /> <img id="imgPend" src="Pend.gif" style="position: absolute;" /> </body> … Sub Swing() Dim a Dim arm ang = ang + speed If ang > 0.5 Or ang < -0.5 Then speed = -speed End If imgPend.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * 150 imgPend.style.pixelTop = imgMid.style.pixelTop + cos(ang) * 150 For a = 1 To 9 Set arm = document.getElementById("imgArm" & a) arm.style.pixelLeft = imgMid.style.pixelLeft + sin(ang) * (a * 15) arm.style.pixelTop = imgMid.style.pixelTop + cos(ang) * (a * 15) Next End Sub </script> 45 lines of code

  11. Example: Total • Real Power of loops • using counter variable • do something slightly different each time • Example: Option Explicit Dim num Dim tot tot = 0 For num = 1 To 4 tot = tot + num Next lblRes.InnerText = tot

  12. Example: Total

  13. Question: For … Next • What does the following code display in parNums: Dim s Dim counter s = "" For counter = 1 To 10 s = s & " " & counter Next parNums.innerText = s 1 2 3 4 5 6 7 8 9 10

  14. Question: For … Step … Next • What does the following code display in parNums: Dim s Dim i s = "" For i = 24 To 12 Step -2 s = s & " " & i Next parNums.innerText = s 24 22 20 18 16 14 12

  15. Example: Letter Count <script language=vbscript> Option Explicit Sub btnCount_OnClick() Dim pos Dim count Dim char count = 0 For pos = 1 To Len(txtWords.value) char = Mid(txtWords.value, pos, 1) If char = "e" Then count = count + 1 End If Next lblCount.innerText = count End Sub </script>

  16. Example: Shades <script language="vbscript"> Option Explicit Sub btnShow_OnClick() Const stTag = "<span style=""background: #" Dim h, p, msg, red msg = txtMsg.value h = "" red = 255 For p = 1 To Len(msg) h = h + stTag + Hex(red) + "0000"">" h = h + Mid(msg, p, 1) h = h + "</span>" red = red - 5 Next divTones.innerHTML = h End Sub </script>

  17. Do ... Loop statement • repeat code unknown number of times • more flexible than For • slower than For • Syntax (Do Until):DoUntilcondition statementblock Loop • Syntax (Do While):DoWhilecondition statementblock Loop

  18. Example: Do … Loop • Can do everything a For … Loop can:Dim I Dim i i = 1 Do While i <= 10 For i = 1 To 10lblN.InnerText = ipicN.InnerText = i i = i + 1 Loop Next • And more:Dim i i = 1 Do While i < 10 lblN.innertext = i If (i / 2) = Int(i / 2) then i = i + 1 Else i = i + 3 End If Loop

  19. Question: Do … Loop • What does the following display in parNums: Dim s Dim num s = "" num = 10 Do While num > -6 s = s & " " & num num = num - 1.5 Loop parNums.innerText = s 10 8.5 7 5.5 4 2.5 1 -0.5 -2 -3.5 -5

  20. Question: Do … Loop • What does the following display in parNums: Dim num num = 6 Do Until num > 4 num = num + 5 parNums.innerText = parNums.innerText & num Loop nothing, 6 is already greater than 4

  21. Tutorial Exercise: Hello • Task 1: Get the Hello Examples (0 to 2) working. • Task 2: Modify your page so that it uses a variable to temporarily build to html. • Task 3: Modify your page so that the user can control how many 'Hellos' appear.

  22. Tutorial Exercise: Pendulum • Task 1: Get the Pendulum examples (1 to 3) working. • Task 2: Increase the number of dots for the arm. • Task 3: Modify your code so that the arm and pendulum are centred correctly.hint: deduct half the width of the image.

  23. Tutorial Exercise: Letter Count • Task 1: Get the Letter Count Example (from the lecture) working. • Task 2: Modify your Letter Count page, so that the user can control which letter is counted.Hint: You will need a text box for the user to type a letter into. • Task 3: Modify your Letter Count program, so that the user cannot type more than one letter in the letter text box.Hint: Use the text box’s change event, and the len function.

  24. Tutorial Exercise: Vowel Count • Task 1: Create a new page that counts the number of vowels (a, e, i, o, u) in a piece of text.Hint: similar to the letter count example.

  25. Tutorial Exercise: Shades • Task 1: Get the shades example from the lecture working. • Task 2: Modify the page so that it puts a space in between each letter. • Task 3: Change the program so that it uses shades of another colour instead. • Task 4: Create a new page that selects random shades of your selected colour. Hint: use the Rnd function.

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