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11 – Array Variables

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Questions: Loops• What is the value of t, after this code

executes? t = 0; for (x = 4; x <= 6; x++){ t = t + x; }

15

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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>";

var f;for (f = 1; f<=7; f++){ parFaces.innerHTML = parFaces.innerHTML + "<img src=face.jpg>";}

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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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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

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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 v0var n;

function btnStart_onClick(){ n = 1 + parseInt(Math.random() * 10) if (n == 1){ parQuest.innerText = "What is eins?"; }else{ if (n == 2){ parQuest.innerText = "What is zwei?"; }else{ if (n == 3){ parQuest.innerText = "What is drei?"; }else{ if (n == 4){ parQuest.innerText = "What is vier?"; }else{ if (n == 5){ parQuest.innerText = "What is funf?"; }else{ if (n == 6){ parQuest.innerText = "What is sechs?"; }else{ if (n == 7){ parQuest.innerText = "What is sieben?"; }else{ if (n == 8){ parQuest.innerText = "What is acht?"; }else{ if (n == 9){ parQuest.innerText = "What is neun?"; }else{ if (n == 10){ parQuest.innerText = "What is zehn?"; } } } } } } } } } } } function btnCheck_onClick(){ if (parseInt(txtAns.value) == n){ parRes.innerText = "Correct!"; }else{ parRes.innerText = "Sorry, please try again." + n; } }

function btnStart_onClick(){ n = 1 + parseInt(Math.random() * 10) if (n == 1){ parQuest.innerText = "What is eins?"; }else{ if (n == 2){ parQuest.innerText = "What is zwei?"; }else{ if (n == 3){ parQuest.innerText = "What is drei?"; }else{ if (n == 4){ parQuest.innerText = "What is vier?"; }else{ if (n == 5){ parQuest.innerText = "What is funf?"; }else{ if (n == 6){ parQuest.innerText = "What is sechs?"; }else{ if (n == 7){ parQuest.innerText = "What is sieben?"; }else{ if (n == 8){ parQuest.innerText = "What is acht?"; }else{ if (n == 9){ parQuest.innerText = "What is neun?"; }else{ if (n == 10){ parQuest.innerText = "What is zehn?"; } } } } } } } } } } }

• Pick random number

• Use If statements– one inside another

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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

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Array Variables (Declaration)

• General syntax:

var varname = new Array(lastElement);

• Specific examples:

var HR = new Array(16); var x = new Array(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;

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Questions: ArraysConsider the following code:

var x;

var res;

var age = new Array(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)

var Name = new Array(4);

Name[0] = "Bob"; Name[1] = "Sally"; Name[2] = "Jo"; Name[3] = "Fred"; Name[4] = "Alison";

var Name1;var Name2;var Name3;var Name4;var Name5; Name1 = "Bob"; Name2 = "Sally"; Name3 = "Jo"; Name4 = "Fred"; Name5 = "Alison";

Single array declaration5 variable declarations

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Arrays: why? (use)

var Num; Num = parseInt(Math.random() * 5); Res = Name[Num];

var Num; Num = parseInt(Math.random() * 5) if (Num == 0){ Res = Name1; }else if (Num == 1){ Res = Name2; }else if (Num == 2){ Res = Name3; }else if (Num == 3){ Res = Name4; }else{ Res = Name5; }

Single line of code picks any element

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Example: German Numbers v1var Nums = new Array(10);var n; function window_onLoad(){ 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"; } function btnStart_onClick(){ n = 1 + parseInt(Math.random() * 10); parQuest.innerText = "What is " + Nums[n] + "?"; } function btnCheck_onClick(){ if (parseInt(txtAns.value) == n){ parRes.innerText = "Correct!"; }else{ parRes.innerText = "Sorry, please try again." + n; } }

ArrayDeclaration

ArrayUse

ArrayAssignment

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Example: German Numbers v0 vs. v1var Nums = new Array(10);var n; function window_onLoad(){ 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"; } function btnStart_onClick(){ n = 1 + parseInt(Math.random() * 10); parQuest.innerText = "What is " + Nums[n] + "?"; } function btnCheck_onClick(){ if (parseInt(txtAns.value) == n){ parRes.innerText = "Correct!"; }else{ parRes.innerText = "Sorry, please try again." + n; } }

var n;

function btnStart_onClick(){ n = 1 + parseInt(Math.random() * 10) if (n == 1){ parQuest.innerText = "What is eins?"; }else{ if (n == 2){ parQuest.innerText = "What is zwei?"; }else{ if (n == 3){ parQuest.innerText = "What is drei?"; }else{ if (n == 4){ parQuest.innerText = "What is vier?"; }else{ if (n == 5){ parQuest.innerText = "What is funf?"; }else{ if (n == 6){ parQuest.innerText = "What is sechs?"; }else{ if (n == 7){ parQuest.innerText = "What is sieben?"; }else{ if (n == 8){ parQuest.innerText = "What is acht?"; }else{ if (n == 9){ parQuest.innerText = "What is neun?"; }else{ if (n == 10){ parQuest.innerText = "What is zehn?"; } } } } } } } } } } } function btnCheck_onClick(){ if (parseInt(txtAns.value) == n){ parRes.innerText = "Correct!"; }else{ parRes.innerText = "Sorry, please try again." + n; } }

v0 v1

25 lines

50 lines

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Error: Subscript Out of Range• Index too big/small

var x = new Array(3); x[0] = 9; x[1] = 5; x[2] = 21; x[3] = 23; x[4] = 12; x = 5;

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Error: Type mismatch• index missing

var x = new Array(3); x[0] = 9; x[1] = 5; x[2] = 21; x[3] = 23; x = 5;

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Error: Type mismatch• index given for non-array variable: b

var x = new Array(3);var b; x[0] = 9; x[1] = 5; x[2] = 21; x[3] = 23; b[3] = 12;

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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

var Books = new Array(55);

Books[17] = 45;

if (Books[11] >6){ document.bgColor = "red";}

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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

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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

var Country = new Array(4);var City = new Array(4);var Num;

function 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"; }

function btnStart_onClick(){ Num = 1 + parseInt(Math.random() * 3); parQuest.innerText = "What is the capital of " + Country[Num] + "?"; }

• 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:

if (txtNum.value == City[Num]){

var Country = new Array(4);var City = new Array(4);var Num;

function 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"; }

function btnStart_onClick(){ Num = 1 + parseInt(Math.random() * 3); parQuest.innerText = "What is the capital of " + Country[Num] + "?"; }

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Example: Drinks v1

Clears array

Displays array

Total of array

Searches array

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Example: Drinks v1 var Units = new Array(6); var curUnit;

function window_onLoad(){ curUnit = 0; }

function btnAdd_onClick(){ Units[curUnit] = parseInt(txtUnit.value); curUnit = curUnit + 1; }

function 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; }

function 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]; }

….

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Example: Drinks v1 ….

function btnTotal_onClick(){ var 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; }

function btnFind_onClick(){ if (txtUnit.value == Units[0]){ lblRes.innerText = "Found in slot 0"; }else if (txtUnit.value == Units[1]){ lblRes.innerText = "Found in slot 1"; }else if (txtUnit.value == Units[2]){ lblRes.innerText = "Found in slot 2"; }else if (txtUnit.value == Units[3]){ lblRes.innerText = "Found in slot 3"; }else if (txtUnit.value == Units[4]){ lblRes.innerText = "Found in slot 4"; }else if (txtUnit.value == Units[5]){ lblRes.innerText = "Found in slot 5"; }else if (txtUnit.value == Units[6]){ lblRes.innerText = "Found in slot 6"; }else{ lblRes.innerText = "Not Found"; } }

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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

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

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Example: Drinks v2 (Total)

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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 while loop, new value different from previous

• Task 6: Modify your page so that it plays appropriate sounds when the user gets the answer right/wrong

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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

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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).