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08 – Iterative Execution

08 – 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:

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08 – Iterative Execution

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  1. 08 – 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: • To be able to implement code that does repetitive tasks, using looping structures: • known limits (for loop) • unknown limits (do loop)

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

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

  5. For ... Next statement • repeat code known number of times • reduces length of code • easier to change • Syntax:Forcounter=startToend [statementblock]Next

  6. 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 lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" Next End Sub </script>

  7. Advantages • Less code: • This makes program: • Easier to read • Easier to change (imagine 50 Hellos) Hello v1 Hello v2 Option Explicit Sub btnGo_OnClick() lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" End Sub Option Explicit Sub btnGo_OnClick() Dim h For h = 1 To 10 lblHello.innerHTML = lblHello.innerHTML & "Hello<br>" Next End Sub 10lines 4 lines

  8. Example: Total • Real Power of loops • using counter variable • do something slightly different each time • Example: Dim num Dim tot tot = 0 For num = 1 To 5 tot = tot + num Next lblRes.InnerText = tot

  9. Example: Total

  10. Question: For … Next • What does the following code produce: Dim counter For counter = 1 To 10 lblNums.InnerText = lblNums.InnerText & counter Next • What does the following code produce: Dim i For i = 24 To 8 Step -2 lblNums.InnerText = lblNums.InnerText & i & i * 2 Next

  11. 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>

  12. Example: Drinks v1 <script language=VBScript> Dim Units(6) Dim curUnit Sub Window_OnLoad() curUnit = 0 End Sub Sub btnAdd_OnClick() Units(curUnit) = txtUnit.value curUnit = curUnit + 1 End Sub Sub btnClear_OnClick() Units(0) = 0 Units(1) = 0 Units(2) = 0 Units(3) = 0 Units(4) = 0 Units(5) = 0 Units(6) = 0 curUnit = 0 End Sub Sub btnShow_OnClick() lblRes.innerText = "" lblRes.innerText = lblRes.innerText & Units(0) & " " lblRes.innerText = lblRes.innerText & Units(1) & " " lblRes.innerText = lblRes.innerText & Units(2) & " " lblRes.innerText = lblRes.innerText & Units(3) & " " lblRes.innerText = lblRes.innerText & Units(4) & " " lblRes.innerText = lblRes.innerText & Units(5) & " " lblRes.innerText = lblRes.innerText & Units(6) End Sub ….

  13. Example: Drinks v1 …. Sub btnTotal_OnClick() Dim total total = 0 total = total + Units(0) total = total + Units(1) total = total + Units(2) total = total + Units(3) total = total + Units(4) total = total + Units(5) total = total + Units(6) lblRes.innerText = total End Sub Sub btnFind_OnClick() If txtUnit.value = Units(0) Then lblRes.innerText = "Found in slot 0" ElseIf txtUnit.value = Units(1) Then lblRes.innerText = "Found in slot 1" ElseIf txtUnit.value = Units(2) Then lblRes.innerText = "Found in slot 2" ElseIf txtUnit.value = Units(3) Then lblRes.innerText = "Found in slot 3" ElseIf txtUnit.value = Units(4) Then lblRes.innerText = "Found in slot 4" ElseIf txtUnit.value = Units(5) Then lblRes.innerText = "Found in slot 5" ElseIf txtUnit.value = Units(6) Then lblRes.innerText = "Found in slot 6" Else lblRes.innerText = "Not Found" End If End Sub </script>

  14. Example: Drinks v2 <script language=VBScript> Dim Units(6) Dim curUnit Sub Window_OnLoad() curUnit = 0 End Sub Sub btnAdd_OnClick() Units(curUnit) = txtUnit.value curUnit = curUnit + 1 End Sub Sub btnClear_OnClick() Dim i For i = 0 To 6 Units(i) = 0 Next curUnit = 0 End Sub Sub btnShow_OnClick() Dim i lblRes.innerText = "" For i = 0 To 6 lblRes.innerText = lblRes.innerText & Units(i) & ", " Next End Sub …

  15. Do ... Loop statement • repeat code unknown number of times • more flexible than For • slower than For • Syntax:Do [{While|Until} condition] [statementblock] Loop

  16. 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

  17. Question: Do … Loop • What does the following produce: Dim num num = 20 Do While num > -12 lblDo.InnerText = lblDo.InnerText & num num = num - 1.5 Loop • What does the following produce: Dim num num = 6 Do Until num > 4 num = num + 5 lblDo.InnerText = lblDo.InnerText & num Loop

  18. Tutorial Exercise • Task 1: Get the Hello Example (from the lecture) working. • Task 2: Modify your page so that the user can control how many 'Hellos' appear. • Task 3: Get the Letter Count Example (from the lecture) working. • Task 4: 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 5: 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.

  19. Tutorial Exercise • Task 1: Get the Drinks v2 example (from the lecture) working. You have the code for Add, Clear, & Show but not for Total and Find • Task 2: Modify your page so that it displays a meaningful message when all elements of the array are used up.

  20. Tutorial Exercise • Task 1: Modify the German numbers page (from last week) to prevent same random number appearing twice • store used numbers • use Do Until new value different from previous

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