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Mark Dixon Page 1
10 – Array Variables
Mark Dixon Page 2
T1 – In-class test• Results mixed:
– quite a few fails 26% (17/65)– some very good (85% max)
• ask more questions in tutorials
• do you understand?– understand roughly (follow when it is explained)– deep understanding, could you explain it in
detail to someone else?
• don't just copy code
• do all exercises, ask for help (expected)
0123456789101112131415161718
fail 3 2:2 2:1 1
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Questions: Loops• What is the value of t, after this code
executes? t = 0 For x = 4 To 6 t = t + x Next
15
Mark Dixon Page 4
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 fFor f = 1 To 7 parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>"Next
Mark Dixon Page 5
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
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Inefficient Code• duplication in both branches of if
If weight > 2.2 Then x = 5 x = 5 Else x = 5 End If
• unused variable declarationsDim x Dim xDim y x = 5 x = 5
• redundant (nil effect) lines of code x = 23 x = 5 x = 5
Mark Dixon Page 7
Example: German Numbers•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)
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
Mark Dixon Page 8
Example: German Numbers• Problem: can't directly pick random word• Can: pick random number
1 – eins2 – zwei3 – drei4 – vier5 – funf6 – sechs7 – sieben8 – acht9 – neun10 – zehn
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Example: German Numbers v0Option Explicit Dim n
Sub Window_onLoad() Randomize End Sub
Sub btnStart_onClick() n = 1 + Int(Rnd() * 10) 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(Rnd() * 10) 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
Mark Dixon Page 10
Array Variables (what)
Value
141
151
143
155
139
127
134
• multiple values– stored in single variable
Index
6
5
4
3
2
1
0
• index – identifies individual values (called elements)
• the value of element 3 is 155
• last element
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Arrays Variables
Mark Dixon Page 12
Array Variables (Declaration)
• General syntax:
Dim varname(lastElement)
• Specific examples:
Dim HR(16) Dim x(8)
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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
Mark Dixon Page 14
Questions: ArraysConsider 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
15.37
age
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Arrays: why? (declaration)
Dim Name(4)
Name(0) = "Bob" Name(1) = "Sally" Name(2) = "Jo" Name(3) = "Fred" Name(4) = "Alison"
Dim Name1Dim Name2Dim Name3Dim Name4Dim Name5 Name1 = "Bob" Name2 = "Sally" Name3 = "Jo" Name4 = "Fred" Name5 = "Alison"
Single array declaration5 variable declarations
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Arrays: why? (use)
Dim Num Num = Int(Rnd() * 5) Res = Name(Num)
Dim Num Num = Int(Rnd() * 5) 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
Single line of code picks any element
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Example: German Numbers v1Option 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(Rnd() * 10) 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
ArrayDeclaration
ArrayUse
ArrayAssignment
Mark Dixon Page 18
Example: German Numbers v0 vs. v1Option 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(Rnd() * 10) 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
Option Explicit Dim n
Sub window_onLoad() Randomize End Sub
Sub btnStart_onClick() n = 1 + Int(Rnd() * 10) 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
v0 v1
27 lines
54 lines
Mark Dixon Page 19
Error: Subscript Out of Range• Index too big/small
Option ExplicitDim x(3) x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 x(4) = 12 x = 5
Mark Dixon Page 20
Error: Type mismatch• index missing
Option ExplicitDim x(3) x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 x = 5
Mark Dixon Page 21
Error: Type mismatch• index given for non-array variable: b
Option ExplicitDim x(3)Dim b x(0) = 9 x(1) = 5 x(2) = 21 x(3) = 23 b(3) = 12
Mark Dixon Page 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 Then document.bgColor = "red"End If
Mark Dixon Page 23
Example: Capital CitiesSPECIFICATION
• 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
Mark Dixon Page 24
Example: Capital Cities• Two arrays – stored in same order:
Country City
0 UK
1 France
2 Spain
3 Greece
0 London
1 Paris
2 Madrid
3 Athens
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Example: Capital Cities
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
• How many array:– declarations?– assignments?
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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
Mark Dixon Page 27
Example: Drinks v1
Clears array
Displays array
Total of array
Searches array
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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() 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
….
Mark Dixon Page 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) 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
Mark Dixon Page 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
Mark Dixon Page 31
Example: Drinks v2 (Reset)• Use loop counter variable (i) as array index:
Mark Dixon Page 32
Example: Drinks v2 (Total)
Mark Dixon Page 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
Mark Dixon Page 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
Mark Dixon Page 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).