Variables & Data Variables & Data typestypes

Flash ActionScript Flash ActionScript 3.03.0

Introduction toIntroduction to

Thomas Lövgren, Flash developer

thomas.lovgren@humlab.umu.se

Variables A variable is a place to store informationA variable is a place to store information It has a name and a typeIt has a name and a type Variables are used to make the code dynamicVariables are used to make the code dynamic Values can generally be accessed or changed at any timeValues can generally be accessed or changed at any time An identifier (usually a letter, word, or phrase) that is An identifier (usually a letter, word, or phrase) that is

linked to a value stored in the system's memory or an linked to a value stored in the system's memory or an expression that can be evaluatedexpression that can be evaluated

Depending on the type system of a programming Depending on the type system of a programming language, variables may only be able to store a specified language, variables may only be able to store a specified data typedata type

Naming variablesNaming variables Variable names can only contain letters, numbers, Variable names can only contain letters, numbers,

and dollar signs ($)and dollar signs ($) All variables must have unique namesAll variables must have unique names Start variables with a lowercase letterStart variables with a lowercase letter Variables are Variables are case-sensitivecase-sensitive Use mixed case for concatenated wordsUse mixed case for concatenated words Don't use reserved words: Don't use reserved words: this, menu, private, video, this, menu, private, video,

etc.etc. Don't use the same variable name with different Don't use the same variable name with different

casescases Keep variables as short as possible while retaining Keep variables as short as possible while retaining

clarityclarity

Example, with strict datatypingExample, with strict datatyping::var xSpeed:Number;var xSpeed:Number;

Data typesData types The The Data type Data type defines the type of data a variable defines the type of data a variable

or ActionScript element can holdor ActionScript element can hold

Primitive data types (Primitive data types (Top level data typesTop level data types): : Boolean, int, Null, Number, String, uint, Boolean, int, Null, Number, String, uint,

and voidand void

Complex data types: Complex data types: Object, Array, Date, Error, Function, Object, Array, Date, Error, Function,

RegExp, XML, and XMLListRegExp, XML, and XMLList

Variable syntaxVariable syntax Example of the different parts and structure of a Example of the different parts and structure of a

variable declaration/populationvariable declaration/population

Data type: String (1/2)Data type: String (1/2) Strings are sequences of characters, numbers and Strings are sequences of characters, numbers and

punctuation marks. These are enclosed within punctuation marks. These are enclosed within double (") quotation marksdouble (") quotation marks

The String data type represents a sequence of 16-bit The String data type represents a sequence of 16-bit characterscharacters

The default value for a variable declared with the The default value for a variable declared with the String data type is nullString data type is null

//declaration//declarationvar myURL_string:String;var myURL_string:String;

//assignment//assignmentmyURL_string = "www.flashkit.com";myURL_string = "www.flashkit.com";

//declaration and assignment//declaration and assignmentvar myURL_string:String = "www.flashkit.com";var myURL_string:String = "www.flashkit.com";

Example of some methods for the Example of some methods for the String objectString object are: are:Substring, charAt, replace, toUpperCase, split, Substring, charAt, replace, toUpperCase, split, joinjoin etc etc

//declare variable//declare variablevar my_string:String;var my_string:String;

//assignment and concatenation//assignment and concatenationmy_stringmy_string = ”Hi ”+”there!”; = ”Hi ”+”there!”; //traces to Hi there!//traces to Hi there!

//getting substring//getting substringvar sub_string:String = var sub_string:String = my_stringmy_string.substring(3, .substring(3, my_stringmy_string.length);.length);

//making all characters uppercase//making all characters uppercasevar upper_string:String = sub_string.toUpperCase();var upper_string:String = sub_string.toUpperCase();trace(upper_string); trace(upper_string); //yields THERE!//yields THERE!

Tip! Declare your variables first (on top)Tip! Declare your variables first (on top)

Datatype: String (2/2)Datatype: String (2/2)

Data type: Number (1/2)Data type: Number (1/2) The Number data type can represent integers, The Number data type can represent integers,

unsigned integers, and floating-point numbersunsigned integers, and floating-point numbers The Number data type uses the 64-bit double-The Number data type uses the 64-bit double-

precision formatprecision format The default value is NaNThe default value is NaN

//declaration//declarationvar length:Number;var length:Number;

//assignment//assignmentlength = 1100;length = 1100;length = -22;length = -22;length = 0.00002234;length = 0.00002234;length = 100/3; length = 100/3; //traces to 33.3333333333333//traces to 33.3333333333333length = 1/0; length = 1/0; //traces to Infinity//traces to Infinity

Variable declaration, assignment and initializationVariable declaration, assignment and initialization

//declaration//declarationvar height:Number;var height:Number;

//assignment//assignmentheight = 200;//literal valueheight = 200;//literal valueheight = anotherVariable;//value from another variableheight = anotherVariable;//value from another variable

//initialization(declaration and assignment on the same code line)//initialization(declaration and assignment on the same code line)var width:Number = 300;var width:Number = 300;

//check max and min values//check max and min values Number.MAX_VALUE == 1.79769313486231e+308Number.MAX_VALUE == 1.79769313486231e+308Number.MIN_VALUE == 4.940656458412467e-324Number.MIN_VALUE == 4.940656458412467e-324

Data type: Number (2/2)Data type: Number (2/2)

Data type: intData type: int New data type in AS3New data type in AS3 The The intint data type is a 32-bit integer between - data type is a 32-bit integer between -

2,147,483,648 and 2,147,483,6472,147,483,648 and 2,147,483,647 Integers only work in whole numbers and ignore the Integers only work in whole numbers and ignore the

decimal value, always rounding downdecimal value, always rounding down The default value for variables that are of data type The default value for variables that are of data type

uint is 0uint is 0

//example 1//example 1

var myInt:int = -15;var myInt:int = -15;

var myInt2:int = 3500;var myInt2:int = 3500;

//example 2//example 2

var num:int = 2.5;var num:int = 2.5;

var product:int = num + 2;var product:int = num + 2;

trace(product); trace(product); //4, the decimal will be ignored//4, the decimal will be ignored

Data type: unitData type: unit New data type in AS3New data type in AS3 The The uintuint (Unsigned Integer) data type is a 32-bit (Unsigned Integer) data type is a 32-bit

unsigned integer between 0 and 4,294,967,295unsigned integer between 0 and 4,294,967,295 Unsigned integer or any non-negative whole Unsigned integer or any non-negative whole

numbernumber The default value for variables that are of data The default value for variables that are of data

type uint is 0type uint is 0

var myUnit:unit = 1;var myUnit:unit = 1;

var mySecondUnit:unit = 3500;var mySecondUnit:unit = 3500;

var unsignedInteger:uint; var unsignedInteger:uint; //0//0

Number, int or unit?Number, int or unit?

To maximize performance, it’s recommended that we use the To maximize performance, it’s recommended that we use the Number data type only for integer values Number data type only for integer values largerlarger than the int than the int and uint types can store or for floating-point numbers. and uint types can store or for floating-point numbers.

To store a floating-point number, include a decimal point in To store a floating-point number, include a decimal point in the number the number

If we omit a decimal point, the number will be stored as an If we omit a decimal point, the number will be stored as an integerinteger

Data type: BooleanData type: Boolean Boolean represents a boolean value, possible Boolean represents a boolean value, possible

values: values: truetrue or or falsefalse Converts the parameter expression to a Boolean Converts the parameter expression to a Boolean

value and returns true or falsevalue and returns true or false Default vaule is Default vaule is falsefalse

//declaration of a boolean variable//declaration of a boolean variable

var isLoaded:Boolean;var isLoaded:Boolean;

//assignmet//assignmet

isLoadedisLoaded = true; = true;

Default Values (1/2)Default Values (1/2) A A Default value Default value is the value that a variable is the value that a variable

contains before you set its valuecontains before you set its value You You initialize initialize a variable when you set its value a variable when you set its value

for the first timefor the first time If you declare a variable, but do not set its value, If you declare a variable, but do not set its value,

that variable is that variable is uninitializeduninitialized The value of an uninitialized variable depends on The value of an uninitialized variable depends on

its data typeits data type

Default Values (2/2)Default Values (2/2) The following table describes the default values of The following table describes the default values of

variables, organized by data typevariables, organized by data type

NoteNote! For variables of type Number, the default value is NaN (not a ! For variables of type Number, the default value is NaN (not a number)number)

Array (1/2)Array (1/2) Arrays are lists of data under which each item is Arrays are lists of data under which each item is

identified by its order within the listidentified by its order within the list The first element in an Array has index 0The first element in an Array has index 0 An array can be made up of primitive type values An array can be made up of primitive type values

like strings, numeric values, booleans or complex like strings, numeric values, booleans or complex type values like other arrays or objectstype values like other arrays or objects

var music_array:Array = new Array();var music_array:Array = new Array();

music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron Maiden", "David Gray", "Van Morrison"];Maiden", "David Gray", "Van Morrison"];

music_array.length music_array.length //traces the length of the array//traces the length of the array

music_array[1]; music_array[1]; //traces Bruce Springsteen //traces Bruce Springsteen

var my_array:Array = [5,"Hello!",{a:5, b:7}]; var my_array:Array = [5,"Hello!",{a:5, b:7}]; //complex array//complex array

Array (2/2)Array (2/2) Example of some methods for the Example of some methods for the Array objectArray object are: are:

slice, join, concat, push, pop, reverseslice, join, concat, push, pop, reverse etc. etc.

var music_array:Array = new Array();var music_array:Array = new Array();

music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron Maiden", "David Gray", "Van Morrison"];Maiden", "David Gray", "Van Morrison"];

//slice(startIndex, endIndex)//slice(startIndex, endIndex)

music_array.slice(2,4); music_array.slice(2,4); //traces U2, Iron Maiden//traces U2, Iron Maiden

TypecastingTypecasting Sometimes we need to Sometimes we need to typecast typecast a data type into a data type into

another (for some reson), for exampe if we load another (for some reson), for exampe if we load XML data (numbers) and Flash interpret it like XML data (numbers) and Flash interpret it like string vaulesstring vaules

Here’s an example of how we can typecast a string Here’s an example of how we can typecast a string into a numberinto a number

var my_string:String = "50";var my_string:String = "50";

var my_num:Number = 20;var my_num:Number = 20;

var answer:Number;var answer:Number;

trace(my_string + my_num); trace(my_string + my_num); //traces 5020//traces 5020

//typecast the string to a number data type//typecast the string to a number data type

trace(Number(my_string) + my_num); trace(Number(my_string) + my_num); //traces 70//traces 70

ScopeScope Scope is the realm or space in wich an object Scope is the realm or space in wich an object

(variable) lives(variable) lives In ActionScript 3.0, variables are always assigned In ActionScript 3.0, variables are always assigned

the scope of the function or class in which they are the scope of the function or class in which they are declareddeclared

Entrance into that scope typically begins a variable's Entrance into that scope typically begins a variable's lifetime and exit from that scope typically ends its lifetime and exit from that scope typically ends its lifetimelifetime

function localScope(){ function localScope(){

var strLocal:String = "local"; var strLocal:String = "local";

} }

localScope(); localScope();

trace(strLocal); trace(strLocal); //error because strLocal is not defined globally//error because strLocal is not defined globally

Arithmetic operatorsArithmetic operators Arithmetic operatorsArithmetic operators

+, -, *, /, %+, -, *, /, %

++, - -++, - -

+=, -=, *=, /=, %=+=, -=, *=, /=, %=

Increment ++, and decrement - - Increment ++, and decrement - -

Increments/decrements a variable by 1Increments/decrements a variable by 1var x:Number = 10;var x:Number = 10;

x++;x++;

trace(x); trace(x); //traces 11//traces 11

x--;x--;

trace(x); trace(x); //traces 10//traces 10

PrecedencePrecedence The answer depends on operator precedenceThe answer depends on operator precedence

var i:Number;var i:Number;

i = 12 + 3 * 10 / 2; i = 12 + 3 * 10 / 2; //traces 27//traces 27

You can override precedence by using parentesesYou can override precedence by using parenteses

var i:Number;var i:Number;

i=(12 + 3) * 10 / 2;i=(12 + 3) * 10 / 2;

trace(i); trace(i); //traces 75//traces 75