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

Next iteration 3 true "She said Never! Never! Never! " 4Next 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 Syntaxfor (<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 codeRuns 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 Lincoln17. Andrew Johnson18. Ulysses S. Grant19. Rutherford B Hayes20. James Garfield21. Chester Arthur22. Grover Cleveland23. Benjamin Harrison24. Grover Cleveland25. William McKinley26. Theodore Roosevelt27. William H. Taft28. Woodrow Wilson29. Warren Harding30. Calvin Coolidge

31. Herbert Hoover32. Franklin D.

Roosevelt33. Harry S. Truman34. Dwight Eisenhower35. John Kennedy36. Lyndon Johnson37. Richard Nixon38. Gerald Ford39. James Carter40. Ronald Reagan41. George H. W. Bush42. William Clinton43. George W. Bush44. Barack Obama


1. George Washington2. John Adams3. Thomas Jefferson4. James Madison5. James Monroe6. John Quincy Adams7. Andrew Jackson8. Martin Van Buren9. William Harrison10. John Tyler11. James Polk12. Zachary Taylor13. Millard Fillmore14. Franklin Pierce15. 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 # elements

var books = new Array(6); with name and elements

var shapes = new

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

2012-05-07


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 up2012-05-07 Katherine Deibel, Fluency in Information Technology 40

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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