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11 – Array Variables

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11 – Array Variables. Questions: Loops. What is the value of t, after this code executes? t = 0; for (x = 4; x <= 6; x++){ t = t + x; }. 15. Questions: Loops.

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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

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>";

}

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
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)
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

Example: German Numbers v0

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?";

}

}

}

}

}

}

}

}

}

}

}

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;

}

}

• Pick random number
• Use If statements
• one inside another
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
Array Variables (Declaration)
• General syntax:var varname = new Array(lastElement);
• Specific examples: var HR = new Array(16); var x = new Array(8);
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;
Questions: Arrays

Consider 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

age

15.37

Arrays: why? (declaration)

5 variable declarations

Single array declaration

var Name1;

var Name2;

var Name3;

var Name4;

var Name5;

Name1 = "Bob";

Name2 = "Sally";

Name3 = "Jo";

Name4 = "Fred";

Name5 = "Alison";

var Name = new Array(4);

Name[0] = "Bob";

Name[1] = "Sally";

Name[2] = "Jo";

Name[3] = "Fred";

Name[4] = "Alison";

Arrays: why? (use)

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;

}

var Num;

Num = parseInt(Math.random() * 5);

Res = Name[Num];

Single line of code picks any element

Example: German Numbers v1

var 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;

}

}

Array

Declaration

Array

Assignment

Array

Use

Example: German Numbers v0 vs. v1

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;

}

}

var 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;

}

}

v0

v1

25 lines

50 lines

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;

Error: Type mismatch
• index missing

var x = new Array(3);

x[0] = 9;

x[1] = 5;

x[2] = 21;

x[3] = 23;

x = 5;

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;

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";

}

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
Example: Capital Cities
• Two arrays – stored in same order:

Country

City

Example: Capital Cities
• How many array:
• declarations?
• assignments?

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] + "?";

}

Question: Arrays
• Write a statement that will decide whether the answer given by the user is correct:

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] + "?";

}

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

Example: Drinks v1

Total of array

Clears array

Displays array

Searches array

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];

}

….

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";

}

}

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