09 – iterative execution

Mark Dixon

09 – Iterative Execution

Mark Dixon

Questions: Variables• Write a line of VBScript code to declare a

variable called h

• Write a line of VBScript code that: 1) reads the value of the variable called h 2) adds 1, and 3) puts the result back into h

Dim h

h = h + 1

Mark Dixon

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

Mark Dixon

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)

Mark Dixon

Example: Hello v1

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

• 1 user click: 10 Hellos (10 lines of code)Lots of lines

imagine 300 Hellos

Mark Dixon

Example: Hello v2

Option Explicit

Sub btnHello_OnClick() Dim h h = 1 Do Until h > 10 lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" h = h + 1 Loop End Sub

• 1 user click: 10 Hellos (6 lines of code)

Mark Dixon

Hello v2: Do Loop• variable h – used as counter

Mark Dixon

Example: Hello v3

Option Explicit

Sub btnHello_OnClick() Dim h For h = 1 To 10 parHello.innerHTML = parHello.innerHTML & "Hello<br>" Next End Sub

• 1 user click: 10 Hellos (4 lines of code)

Mark Dixon

Hello v3: For Loop• variable h – set and incremented

automatically

Mark Dixon

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 v3

4 lines

10lines

Mark Dixon

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

Mark Dixon

For ... Next statement• repeat code known number of times

– reduces length of code

– easier to change

• Syntax:

For variable = start To end statementblock Next

Mark Dixon

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

Mark Dixon

• 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

Mark Dixon

Example: Letter Count <script language=vbscript> Option Explicit

Sub btnCount_OnClick() Dim count Dim pos 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>

Mark Dixon

Letter Count• Search Algorithm:

1) Start at first letter 2) If no more letters then go to 5 3) If letter is an e then add 1 to count 4) Go to 2 5) Display count

Mark Dixon

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

Mark Dixon

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>

Mark Dixon

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

Mark Dixon

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

Mark Dixon

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>

Mark Dixon

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

Mark Dixon

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

Mark Dixon

Loops: Errors


Sub window_onload() For x = 1 To 10 Next End Sub</script>

Mark Dixon

Loops: Errors


Sub window_onload() Dim x For x = 1 To 10 End Sub</script> Statement Expected

(missing Next)

Mark Dixon

Loops: Errors


Sub window_onload() Dim x Next End Sub</script>

Mark Dixon

Loops: Errors


Sub window_onload() Dim x For x = 1 To 10 Next End Sub</script>

Mark Dixon

Tutorial Exercise: Hello• LEARNING OBJECTIVE:

use variables to make a for loop more flexible

• 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.

Mark Dixon

Tutorial Exercise: Letter Count• LEARNING OBJECTIVE:

use a loop to search through a string (text)

• 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 into.

• Task 3: Modify your code so that it responds immediately. Hint: Remove the button, and link your code to the KeyUp event of the text box.

• 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 len function.

Mark Dixon

Tutorial Exercise: Vowel Count• LEARNING OBJECTIVE:

build your own page from scratch, using a loop to search a string (piece of text)

• 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.

Mark Dixon

Tutorial Exercise: Pendulum• LEARNING OBJECTIVE:

use a loop to shorten code responsible for visual display

• 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.

Mark Dixon

Tutorial Exercise: Shades• LEARNING OBJECTIVE:

use functions and operators to change the behaviour of code that uses a loop

• 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.

09 – iterative execution

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