07 – iterative execution
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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 - PowerPoint PPT PresentationTRANSCRIPT
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07 – Iterative Execution
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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
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Example: Hello v0
<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>
• 1 user click: 1 Hello (1 line of code)
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Example: Hello v1
<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>
• 1 user click: 10 Hellos (10 lines of code)Lots of lines
imagine 300 Hellos
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Example: Hello v2
<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>
• 1 user click: 10 Hellos (4 lines of code)
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For ... Next statement• repeat code known number of times
– reduces length of code
– easier to change
• Syntax:
For variable = start To end statementblock Next
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Advantages• Less code:
• This makes program:– Easier to read– Easier to change (imagine 500 Hellos)
Option Explicit
Sub btnGo_OnClick()Dim h For h = 1 To 10 parHello.innerHTML = parHello.innerHTML & "Hello<br>" NextEnd Sub
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
Hello v1 Hello v2
10lines
4 lines
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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 ExplicitDim angDim 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>
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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
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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
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• Real Power of loops– using counter variable– do something slightly different each time
• Example: Option ExplicitDim numDim tottot = 0For num = 1 To 4 tot = tot + numNextlblRes.InnerText = tot
Example: Total
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Example: Total
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Question: For … Next• What does the following code display in
parNums:
Dim sDim counter s = "" For counter = 1 To 10 s = s & " " & counter Next parNums.innerText = s
1 2 3 4 5 6 7 8 9 10
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Question: For … Step … Next• What does the following code display in
parNums:
Dim sDim i s = "" For i = 24 To 12 Step -2 s = s & " " & i Next parNums.innerText = s
24 22 20 18 16 14 12
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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>
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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>
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Do ... Loop statement
• repeat code unknown number of times– more flexible than For
– slower than For
• Syntax (Do Until):Do Until condition statementblockLoop
• Syntax (Do While):Do While condition statementblockLoop
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Example: Do … Loop• Can do everything a For … Loop can:
Dim I Dim ii = 1Do While i <= 10 For i = 1 To 10 lblN.InnerText = i picN.InnerText =
i i = i + 1Loop Next
• And more:Dim ii = 1Do While i < 10 lblN.innertext = i If (i / 2) = Int(i / 2) then i = i + 1 Else i = i + 3 End If Loop
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Question: Do … Loop
• What does the following display in parNums:
Dim sDim 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
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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
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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.
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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.
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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.
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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.
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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.