section voting is up vote in your section by thursday, 10pm assignment: 20 pts for voting two...

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Section Voting is up Vote in your section by Thursday, 10pm

Assignment: 20 pts for voting Two labs this week:

Web App Design Lab

Coin Flipping Lab You decide the order that you do them

2012-05-07 Katherine Deibel, Fluency in Information Technology 1

Arrays & IterationGoing beyond one

Fluency with Information Technology

INFO100 and CSE100

Katherine Deibel


Learning Programming

Programmer Braggery:How many languages do you know? The answer really does not matter

Many languages are regional dialects of each other (share syntax and concepts) Javascript, Java, C#, and Visual Basic are all

object-oriented languages

Scottish accent, Southeast U.S. accent, Boston accent, London accent


When faced with a new language…

I look for how to do the following: Declare variables

If-Else statements

Make and use functions

Manipulate strings

Loops and iteration

Arrays


Labs 7 & 8 and Project 2

Today's lecture

The Takeaway:You have learned the basics for working in many different programming languages.

Katherine Deibel, Fluency in Information Technology 5

Definitions

Iteration, or looping, is the process of repetition: looping through a sequence of

statements to repeat them

2012-05-07

Major Types of Repetitions

For loop Run a fixed number of times

While loop Run 0+ times until condition is met

Do while loop Run 1+ times until condition is met


For LoopsDo I need to repeat myself?


For Loop Basic Syntax

for (<initial>; <condition>; <next>){

<statement list>} Program completes the entire

statement sequence of the <statement list> during each iteration


Control Specification

The three operations in the parentheses of the for loop Control the number of times the loop

iterates

by using an iteration variable (must be declared)



How a For Loop Works

Consider a computation on declared variables j and text

2012-05-07

text = "She said ";for ( var j = 1; j <= 3; j = j + 1 ) { text = text + "Never! ";}alert(text);




control specification





initialization





continuation condition





step size or increment





NO SEMICOLONS!!


Processing for Loops

Step One: <initialization> Sets (and maybe declares) the iteration

variable's value for the first iteration of the loop

Initialization is done only once Example: j is declared and set to 1


text = "She said ";for ( var j = 1; j <= 3; j = j + 1 ) {

text = text + "Never! ";}alert(text);


Step Two: <continuation> The <continuation condition> is tested

If true, the statement list is computed.

If false, the <statement list> is skipped and control passes to the statement after the for loop

Example: j <= 3 and text = …





Step Three: <next iteration> The <next iteration> statement is

computed Loop returns to Step Two Example: j = j + 1





Example

2012-05-07


When j j <= 3 text j++

Before loop - - "She said "

First iteration 1 true "She said Never! " 2

Next iteration 2 true "She said Never! Never! " 3

Next iteration 3 true "She said Never! Never! Never! " 4

Next iteration 4 false - -

After loop text == "She said Never! Never! Never! "

A World-Famous Iteration

Most frequently written for loop Easy to see iteration count: Always runs n times Goes from 0 to n-1


for ( var i = 0; i < n; i++ ) {…}

For Loop Syntax: Initialization

The Iteration Variable Must be declared in the loop or in the

code before the loop

Must follow rules for variable identifiers

i, j, and k are the most common choices The Starting Point

Iteration can begin anywhere, including negative numbers


For Loop Syntax: Continuation

Continuation/Termination Test Test is any expression resulting in a

Boolean value (true/false)

Continuation must involve iteration variable to avoid infinite loop



For Loop Syntax: Step Size

The amount of change in the iteration variable from one iteration to the next

Often called the increment or decrement Increment: j = j + 1

Decrement: j = j – 1 Often uses shorthand: j++ or j-- Can be any size

j = j + 5

j -= 2

2012-05-07

Nested for Loop Syntax

for (<initial i>; <condition i>; <next i>)

{

<some statements>

for (<initial j>; <condition j>; <next j>)

{

<some statements>

}<some statements>

}


Three-Level Nested For Loop


for( var i = 1; i <= N_i; i++ ) {

for( var j = 1; j <= N_j; j++ ) {

for( var k = 1; k <= N_k; k++ ) {

}}

}

Syntax vs Logic Errors

There are two ways to go wrong when programming Syntax Errors how the code is written

Logic Errors what the code does Remember: Just writing code that runs

does not mean it runs correctly


for (var j = 5; j > 0; j++) ;{ //statement body}

Syntactically correct code

Runs forever (BAD!)

Complex Loop Conditions

Loop conditions can be fairly complex

The above loop will run 8 times unless total becomes zero or negative first


for (var j = 0; j < 8 && total > 0; j++){ //statement body}

Arrays and IndexesStoring a Collection of Items



What is an Array?

An indexed list of items Indexed means each element in the

list has a number, or index

2012-05-07

What is an Array?

16. Abraham Lincoln

17. Andrew Johnson

18. Ulysses S. Grant

19. Rutherford B Hayes

20. James Garfield

21. Chester Arthur

22. Grover Cleveland

23. Benjamin Harrison

24. Grover Cleveland

25. William McKinley

26. Theodore Roosevelt

27. William H. Taft

28. Woodrow Wilson

29. Warren Harding

30. Calvin Coolidge

31. Herbert Hoover

32. Franklin D. Roosevelt

33. Harry S. Truman

34. Dwight Eisenhower

35. John Kennedy

36. Lyndon Johnson

37. Richard Nixon

38. Gerald Ford

39. James Carter

40. Ronald Reagan

41. George H. W. Bush

42. William Clinton

43. George W. Bush

44. Barack Obama


1. George Washington

2. John Adams

3. Thomas Jefferson

4. James Madison

5. James Monroe

6. John Quincy Adams

7. Andrew Jackson

8. Martin Van Buren

9. William Harrison

10. John Tyler

11. James Polk

12. Zachary Taylor

13. Millard Fillmore

14. Franklin Pierce

15. James Buchanan


Indexing

Process of creating a sequence of names by associating a base name with a number (like Apollo 13 or Henry VIII)

Each indexed item is called an element of the base-named sequence

2012-05-07

Indexing and Iteration

Index Syntax Index number is enclosed in square

brackets [ ] Iterations can be used to refer to all

elements of a name A[j] for successive iterations over j

referring to different elements of A



Where is the first element?

Index Origin The point at which indexing begins (the

least index) First element

In life, the first element may begin with 1, or have no number (Queen Elizabeth)

JavaScript and most programming languages always uses index origin 0

2012-05-07


JS Syntax for Arrays

with name and # elementsvar books = new Array(6);

with name and elementsvar shapes

= new Array("square","circle","triangle");

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JS Syntax for Arrays (cont.)

Accessing elements in array

shapes[1] is "circle" Changing element in array

shapes[0] = "rectangle"; Adding more elements to the array

shapes[3] = "ellipse";shapes[4] = "heptagon"

orshapes.push("diamond"); adds to the end of the array

2012-05-07


Referring to an Array Element

Referencing an element of the array:shapes[<index>]

Index must be a non-negative integer or expression or variable that resolves to non-negative integer

shapes[1] = …i=3;shapes[i] = …shapes[i+2] = …

2012-05-07


Iteration and Arrays

array.length returns the highest index in the array (the number of elements in it)

2012-05-07

for( var i=0; i<shapes.length; i++){

}


Iteration and Arrays

2012-05-07

var i, text=""; /*declare iteration and other variables*/var fruits = new Array(

'lemons','apples','mangoes','tangerines','kumquats','cantaloupe','peaches','grapefruit','raspberries');

alert("Total number of fruits is " + fruits.length);

for (i=0; i<fruits.length; i++){ text += i + '. ' + fruits[i] + '<br />';}

document.write("<h1>Elements of Fruits Array:</h1><p>" + text + "</p>");

While & Do While LoopsMore looping… <nausea>


Uncertain number of repeats

For loops are good when a fixed number of repetitions is needed

The number of repetitions may not be known a priori

Example: Weight limits on an elevator Get weight of next person in line

If weight plus total so far is less than limit, that person gets on

Once limit is passed, last person gets off and elevator goes up


Example While Loop


/* weights is an array of people's weights limit is the elevator's weight limit */var currWeight = 0;var j = 0;while (weights[j] + currWeight <= limit){

currWeight = currWeight + weights[j];j = j + 1;

}

Do While Loops

In the previous example, the loop would not run if the first person exceeded the weight limit

While loops can run zero or more times Do while loops always run at least once


do {<statements>

} while (condition);

A note about semicolons

Semicolons do NOT go after the loop statement for for loops and while loops


do {<statements>

} while (condition);

for( var i=0; i<n; i++){}

while(x<=maximum){}

There IS a semicolon after the loop statement for a do while loop.

Summary

Loops allow us to repeat steps Arrays are a means for working with

multiple values These are the last of the essential

aspects to programming


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