Arrays II

Robin Burke

IT 130

Outline

Homework #6 Portfolio Array review Array examples Array algorithms Multi-dimensional arrays

Homework #6

Three component grades Knowledge Reasoning Communication

Overall very good papers! Many nice site designs

Issues Target marketing

not really possible for campaign web site you have to identify the audience that will use such a site

not choose the audience and build site to suit Narrow content

site has only policy positions and events easy to find these things

real site would have much more Design justification

report should justify design choices example: information hierarchy

each page has foreground and background what belongs in each category what visual techniques distinguish

Portfolio Must include

new copies of each homework exceptions

if full credit, just copy homework #6 – report only

MS Word .doc or PDF file no "original" needed

Do not include labs homework #6 designs / notes

Due date Midnight, 11/22 (Monday before Thanksgiving)

Portfolio

Do Get started early

you now have enough experience that early assignments should be easy (or at least easier)

Aim for full credit on all assignments send me email if you don't understand the grading feedback

Read the original assignment

Don't Wait until the last minute Ignore what the grader had to say

Portfolio site it130

hwk1 hwk2 ...etc... portfolio

index.html points to old and new assignments

hwk1 hwk2 hwk3 ...etc..

Example

Array

Array is a list of values accessed by index name[index]

foo[5] Must create before usingfoo = new Array ();

Zero-based indexing length attributearr.length

Using for loop to access array

For loop pieces initial counter value: 0 exit test: value < array.length change to counter: + 1

Patternfor (i = 0; i < arr.length; i++)

{

do something to arr[i] element

}

Images array

twodice page from last weekdocument.images[imgNo].src = "dice01.jpg";

How to read this from the document object

the page get the images array

a list of all the images on the page get one item from this array using imgNo as index

some particular image set the src attribute of this image to the given value

Example

n dice

Array algorithms

Common tasks with arrays find an element with some property combine the elements of the array fill an array with values sort the elements

Combination example: average

var total = 0;

for (i = 0; i < numbers.length; i++)

{

total = total + numbers[i];

}

ave = total / numbers.length;

Combination pattern

Assume array contains some values

var variable = empty value;

for (i = 0; i < array.length; i++)

{

variable = accumulate ( variable, array[i] );

}

Example

build-sentence.html Assemble a sentence using the words in an

array words = new Array ("welcome", "to", "arrays",

"in", "JavaScript"); function result = "welcome to arrays in

JavaScript"

Selection example

Find the first element in the array less than zerofor (i = 0; i < array.length; i++)

{

if (array[i] < 0)return i;

}

return -1;

Selection pattern

for (i = 0; i < array.length; i++)

{

if (test (array[i]))

return i; or

return array[i];

}

return not found value;

Selection Example

Find the smallest element of an array A bit different from pattern We have to look at every element

save the best so far

Fill example

Fill an array with zerosfor (i = 0; i < count; i++)

{

array[i] = 0;}

Fill pattern

for (i = 0; i < size; i++)

{

array[i] = initial value;}

Example

Alternate dice idea Fill array with image urls Pick from array instead of if statement

Usually a good idea

Parallel arrays

Sometimes we have data that is paired state / # of electoral votes homework / date due

We can handle this with two arrays same size corresponding indices mean corresponding data

Example

duedate.html

Problem

Easy for arrays to get out of sync Two things to keep track of The pairing is in the programmer's head

not represented in the structure of the data

Multi-dimensional array

We can change our data structure instead of two arrays of elements, which are

paired we can have one array of pairs

Example

Homework #8

Slide show Add rewind, fast-forward, and back buttons Use enable / disable Write a function that controls the buttons so

enable / disable logic is not repeated

Monday

Data representation