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Effective Programming Techniques for Loops and Arrays

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Learn about array variables, loops, and inefficient code practices. Understand array declaration, assignment, and handling multiple valued data efficiently with examples.

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Effective Programming Techniques for Loops and Arrays

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  1. 11 – Array Variables

  2. Questions: Loops • What is the value of t, after this code executes? t = 0 For x = 4 To 6 t = t + x Next 15

  3. Questions: Loops • Simplify the following code, so that it is easy to change the number of faces:parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>" Dim f For f = 1 To 7 parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>" Next

  4. Session Aims & Objectives • Aims • To introduce the main concepts involved in handling more complex (multi valued) data • Objectives,after this week’s sessions, you should be able to: • declare arrays • assign values to array elements • use array elements • use for loops with arrays

  5. Inefficient Code • duplication in both branches of if If weight > 2.2 Then x = 5 x = 5Else x = 5 End If • unused variable declarationsDim x Dim xDim y x = 5 x = 5 • redundant (nil effect) lines of codex = 23 x = 5 x = 5

  6. Example: German Numbers • SPECIFICATION • User Requirements • help people learn German numbers 1 - 10 • Software Requirements • Functional: • show German word for numbers (between 1 and 10) • user enter digits • check if correct • Non-functionalshould be easy to use • User Requirements • describe user's objectivesno mention of technology • Software Requirements • Functional • list facilities to be provided (often numbered) • Non-functional • list desired characteristics(often more subjective)

  7. Example: German Numbers • Problem: can't directly pick random word • Can: pick random number 1 – eins 2 – zwei 3 – drei 4 – vier 5 – funf 6 – sechs 7 – sieben 8 – acht 9 – neun 10 – zehn

  8. Random Numbers 1 + Int( 10 * Rnd() ) 1 0 0.000 0.0000 3 2 2.563 0.2563 6 5 5.678 0.5678 10 9 9.999 0.9999

  9. Example: German Numbers v0 Option Explicit Dim n Sub Window_onLoad() Randomize End Sub Sub btnStart_onClick() n = 1 + Int(10 *Rnd()) If n = 1 Then parQuest.innerText = "What is eins?" Else If n = 2 Then parQuest.innerText = "What is zwei?" Else If n = 3 Then parQuest.innerText = "What is drei?" Else If n = 4 Then parQuest.innerText = "What is vier?" Else If n = 5 Then parQuest.innerText = "What is funf?" Else If n = 6 Then parQuest.innerText = "What is sechs?" Else If n = 7 Then parQuest.innerText = "What is sieben?" Else If n = 8 Then parQuest.innerText = "What is acht?" Else If n = 9 Then parQuest.innerText = "What is neun?" Else If n = 10 Then parQuest.innerText = "What is zehn?" End If End If End If End If End If End If End If End If End If End If End Sub Sub btnCheck_onClick() If CInt(txtAns.value) = n Then parRes.innerText = "Correct!" Else parRes.innerText = "Sorry, please try again." & n End If End Sub Sub btnStart_onClick() n = 1 + Int(10 *Rnd()) If n = 1 Then parQuest.innerText = "What is eins?" Else If n = 2 Then parQuest.innerText = "What is zwei?" Else If n = 3 Then parQuest.innerText = "What is drei?" Else If n = 4 Then parQuest.innerText = "What is vier?" Else If n = 5 Then parQuest.innerText = "What is funf?" Else If n = 6 Then parQuest.innerText = "What is sechs?" Else If n = 7 Then parQuest.innerText = "What is sieben?" Else If n = 8 Then parQuest.innerText = "What is acht?" Else If n = 9 Then parQuest.innerText = "What is neun?" Else If n = 10 Then parQuest.innerText = "What is zehn?" End If End If End If End If End If End If End If End If End If End If End Sub • Pick random number • Use If statements • one inside another

  10. Array Variables (what) Index Value 0 134 1 127 • index – identifies individual values (called elements) 2 139 3 155 4 143 • the value of element 3 is 155 5 151 6 141 • multiple values– stored in single variable • last element

  11. Arrays Variables

  12. Array Variables (Declaration) • General syntax:Dimvarname(lastElement) • Specific examples: Dim HR(16) Dim x(8)

  13. Array Variables (Assignment) • General syntax:arrayname(index)=expression • Specific examples:HR(0) = 134 HR(5) = 151 + b x(5) = 23.87 x(7) = (y + 189.2516) / 2

  14. Questions: Arrays Consider the following code: Dim x Dim res Dim age(2) x = 2 age(0) = 19.6 age(1) = 11.23 age(2) = 15.37 res = age(x) • How many arrays are there? • Name the array(s). • What is in res after the code executes? 1 age 15.37

  15. Arrays: why? (declaration) 5 variable declarations Single array declaration Dim Name1 Dim Name2 Dim Name3 Dim Name4 Dim Name5 Name1 = "Bob" Name2 = "Sally" Name3 = "Jo" Name4 = "Fred" Name5 = "Alison" Dim Name(4) Name(0) = "Bob" Name(1) = "Sally" Name(2) = "Jo" Name(3) = "Fred" Name(4) = "Alison"

  16. Arrays: why? (use) Dim Num Num = Int(5 * Rnd()) If Num = 0 Then Res = Name1 ElseIf Num = 1 Then Res = Name2 ElseIf Num = 2 Then Res = Name3 ElseIf Num = 3 Then Res = Name4 Else Res = Name5 End If Dim Num Num = Int(5 * Rnd()) Res = Name(Num) Single line of code picks any element

  17. Example: German Numbers v1 Option Explicit Dim Nums(10) Dim n Sub Window_onLoad() Randomize Nums(1) = "eins" Nums(2) = "zwei" Nums(3) = "drei" Nums(4) = "vier" Nums(5) = "funf" Nums(6) = "sechs" Nums(7) = "sieben" Nums(8) = "acht" Nums(9) = "neun" Nums(10) = "zehn" End Sub Sub btnStart_onClick() n = 1 + Int(10 * Rnd()) parQuest.innerText = "What is " & Nums(n) & "?" End Sub Sub btnCheck_onClick() If CInt(txtAns.value) = n Then parRes.innerText = "Correct!" Else parRes.innerText = "Sorry, please try again." & n End If End Sub Array Declaration Array Assignment Array Use

  18. Example: German Numbers v0 vs. v1 Option Explicit Dim n Sub window_onLoad() Randomize End Sub Sub btnStart_onClick() n = 1 + Int(10 * Rnd()) If n = 1 Then parQuest.innerText = "What is eins?" Else If n = 2 Then parQuest.innerText = "What is zwei?" Else If n = 3 Then parQuest.innerText = "What is drei?" Else If n = 4 Then parQuest.innerText = "What is vier?" Else If n = 5 Then parQuest.innerText = "What is funf?" Else If n = 6 Then parQuest.innerText = "What is sechs?" Else If n = 7 Then parQuest.innerText = "What is sieben?" Else If n = 8 Then parQuest.innerText = "What is acht?" Else If n = 9 Then parQuest.innerText = "What is neun?" Else If n = 10 Then parQuest.innerText = "What is zehn?" End If End If End If End If End If End If End If End If End If End If End Sub Sub btnCheck_onClick() If CInt(txtAns.value) = n Then parRes.innerText = "Correct!" Else parRes.innerText = "Sorry, please try again." & n End If End Sub Option Explicit Dim Nums(10) Dim n Sub window_onLoad() Randomize Nums(1) = "eins" Nums(2) = "zwei" Nums(3) = "drei" Nums(4) = "vier" Nums(5) = "funf" Nums(6) = "sechs" Nums(7) = "sieben" Nums(8) = "acht" Nums(9) = "neun" Nums(10) = "zehn" End Sub Sub btnStart_onClick() n = 1 + Int(10 * Rnd()) parQuest.innerText = "What is " & Nums(n) & "?" End Sub Sub btnCheck_onClick() If CInt(txtAns.value) = n Then parRes.innerText = "Correct!" Else parRes.innerText = "Sorry, please try again." & n End If End Sub v0 v1 27 lines 54 lines

  19. Error: Subscript Out of Range • Index too big/small Option Explicit Dim x(3) x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 x(4) = 12 x = 5

  20. Error: Type mismatch • index missing Option Explicit Dim x(3) x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 x = 5

  21. Error: Type mismatch • index given for non-array variable: b Option Explicit Dim x(3) Dim b x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 b(3) = 12

  22. Questions: Arrays • Write a line of code that declares an array called Books with 56 elements • Write a line of code that assigns the value 45 to the 18th element of the array. • Write some code that makes the background red, but only when the 12th array element is larger than 6 Dim Books(55) Books(17) = 45 If Books(11) >6 Thendocument.bgColor = "red" End If

  23. Example: Capital Cities • SPECIFICATION • User Requirements • help people learn Capital Cities • Software Requirements • Functional: • ask user for capital of random country • user enter capital • check if correct • Non-functionalshould be easy to use

  24. Example: Capital Cities • Two arrays – stored in same order: Country City

  25. Example: Capital Cities • How many array: • declarations? • assignments? Option Explicit Dim Country(4) Dim City(4) Dim Num Sub window_onLoad() Country(1) = "UK" City(1) = "London" Country(2) = "France" City(2) = "Paris" Country(3) = "Spain" City(3) = "Madrid" Country(4) = "Greece" City(4) = "Athens" Randomize End Sub Sub btnStart_onClick() Num = 1 + CInt(Rnd() * 3) parQuest.innerText = "What is the capital of " & Country(Num) & "?" End Sub

  26. Question: Arrays • Write a statement that will decide whether the answer given by the user is correct: Option Explicit Dim Country(4) Dim City(4) Dim Num Sub window_onLoad() Country(1) = "UK" City(1) = "London" Country(2) = "France" City(2) = "Paris" Country(3) = "Spain" City(3) = "Madrid" Country(4) = "Greece" City(4) = "Athens" Randomize End Sub Sub btnStart_onClick() Num = 1 + CInt(Rnd() * 3) parQuest.innerText = "What is the capital of " & Country(Num) & "?" End Sub If txtNum.value = City(Num) Then

  27. Example: Drinks v1 Total of array Clears array Displays array Searches array

  28. Example: Drinks v1 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() parRes.innerText = "" parRes.innerText = parRes.innerText & Units(0) & " " parRes.innerText = parRes.innerText & Units(1) & " " parRes.innerText = parRes.innerText & Units(2) & " " parRes.innerText = parRes.innerText & Units(3) & " " parRes.innerText = parRes.innerText & Units(4) & " " parRes.innerText = parRes.innerText & Units(5) & " " parRes.innerText = parRes.innerText & Units(6) End Sub ….

  29. 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) parRes.innerText = total End Sub Sub btnFind_onClick() If txtUnit.value = Units(0) Then parRes.innerText = "Found in slot 0" ElseIf txtUnit.value = Units(1) Then parRes.innerText = "Found in slot 1" ElseIf txtUnit.value = Units(2) Then parRes.innerText = "Found in slot 2" ElseIf txtUnit.value = Units(3) Then parRes.innerText = "Found in slot 3" ElseIf txtUnit.value = Units(4) Then parRes.innerText = "Found in slot 4" ElseIf txtUnit.value = Units(5) Then parRes.innerText = "Found in slot 5" ElseIf txtUnit.value = Units(6) Then parRes.innerText = "Found in slot 6" Else parRes.innerText = "Not Found" End If End Sub

  30. Array Algorithms • Common tasks to many programs: • Reset all elements • Display all elements • Total all elements • Search all elements • Find maximum value • Find minimum value • Average • Sort

  31. Example: Drinks v2 (Reset) • Use loop counter variable (i) as array index:

  32. Example: Drinks v2 (Total)

  33. Tutorial Exercise: German Numbers • Task 1: Complete German Numbers Example from lecture.You will need to complete the code for checking the user's answer • Task 2: Modify your page so that it disables and enables the buttons appropriately • Task 3: Modify your page so that the text box gets the focus (cursor) after the start button is pressed • Task 4: Modify your page to allow the user 3 attempts only. • Task 5: Modify your page to prevent same random number appearing twice • store used numbers • use Do Until new value different from previous • Task 6: Modify your page so that it plays appropriate sounds when the user gets the answer right/wrong

  34. Tutorial Exercise: Capital Cities • Task 1: Complete Capital Cities Example from the lecture, adding some more cities.You will need to complete the code for checking the user's answer • Task 2: Modify your page so that it hides and shows the buttons appropriately • Task 3: Modify your page to allow the user 3 attempts only. • Task 4: Modify your page so that it is case in-sensitive (i.e. user can type upper or lower case) • Task 5: Modify your page so that it displays an appropriate picture of the selected capital city. Hint: create another array for the file names. • Task 6: Modify your page so that it plays appropriate sounds when the user gets the answer right/wrong

  35. Tutorial Exercise: Drinks • 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 (not the error dialogue below).

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