Variables%20

1
Variables Data types
Introduction to
Flash ActionScript 3.0
Thomas Lövgren, Flash developer thomas.lovgren_at_hum
lab.umu.se
2
Variables

• A variable is a place to store information
• It has a name and a type
• Variables are used to make the code dynamic
• Values can generally be accessed or changed at
  any time
• An identifier (usually a letter, word, or phrase)
  that is linked to a value stored in the system's
  memory or an expression that can be evaluated
• Depending on the type system of a programming
  language, variables may only be able to store a
  specified data type

3
Naming variables

• Variable names can only contain letters, numbers,
  and dollar signs ()
• All variables must have unique names
• Start variables with a lowercase letter
• Variables are case-sensitive
• Use mixed case for concatenated words
• Don't use reserved words this, menu, private,
  video, etc.
• Don't use the same variable name with different
  cases
• Keep variables as short as possible while
  retaining clarity
• Example, with strict datatyping
• var xSpeedNumber

4
Data types

• The Data type defines the type of data a variable
  or ActionScript element can hold
• Primitive data types (Top level data types)
• Boolean, int, Null, Number, String, uint, and
  void
• Complex data types
• Object, Array, Date, Error, Function, RegExp,
  XML, and XMLList

5
Variable syntax

• Example of the different parts and structure of a
  variable declaration/population

6
Data type String (1/2)

• Strings are sequences of characters, numbers and
  punctuation marks. These are enclosed within
  double (") quotation marks
• The String data type represents a sequence of
  16-bit characters
• The default value for a variable declared with
  the String data type is null
• //declaration
• var myURL_stringString
• //assignment
• myURL_string "www.flashkit.com"
• //declaration and assignment
• var myURL_stringString "www.flashkit.com"

7
Datatype String (2/2)

• Example of some methods for the String object
  are
• Substring, charAt, replace, toUpperCase, split,
  join etc
• //declare variable
• var my_stringString
• //assignment and concatenation
• my_string Hi there! //traces to Hi there!
• //getting substring
• var sub_stringString my_string.substring(3,
  my_string.length)
• //making all characters uppercase
• var upper_stringString sub_string.toUpperCase()
  
• trace(upper_string) //yields THERE!
• Tip! Declare your variables first (on top)

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Data type Number (1/2)

• The Number data type can represent integers,
  unsigned integers, and floating-point numbers
• The Number data type uses the 64-bit
  double-precision format
• The default value is NaN
• //declaration
• var lengthNumber
• //assignment
• length 1100
• length -22
• length 0.00002234
• length 100/3 //traces to 33.3333333333333
• length 1/0 //traces to Infinity

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Data type Number (2/2)

• Variable declaration, assignment and
  initialization
• //declaration
• var heightNumber
• //assignment
• height 200//literal value
• height anotherVariable//value from another
  variable
• //initialization(declaration and assignment on
  the same code line)
• var widthNumber 300
• //check max and min values
• Number.MAX_VALUE 1.79769313486231e308
• Number.MIN_VALUE 4.940656458412467e-324

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Data type int

• New data type in AS3
• The int data type is a 32-bit integer between
  -2,147,483,648 and 2,147,483,647
• Integers only work in whole numbers and ignore
  the decimal value, always rounding down
• The default value for variables that are of data
  type uint is 0
• //example 1
• var myIntint -15
• var myInt2int 3500
• //example 2
• var numint 2.5
• var productint num 2
• trace(product) //4, the decimal will be ignored

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Data type unit

• New data type in AS3
• The uint (Unsigned Integer) data type is a 32-bit
  unsigned integer between 0 and 4,294,967,295
• Unsigned integer or any non-negative whole number
• The default value for variables that are of data
  type uint is 0
• var myUnitunit 1
• var mySecondUnitunit 3500
• var unsignedIntegeruint //0

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Number, int or unit?

• To maximize performance, its recommended that we
  use the Number data type only for integer values
  larger than the int and uint types can store or
  for floating-point numbers.
• To store a floating-point number, include a
  decimal point in the number
• If we omit a decimal point, the number will be
  stored as an integer

13
Data type Boolean

• Boolean represents a boolean value, possible
  values true or false
• Converts the parameter expression to a Boolean
  value and returns true or false
• Default vaule is false
• //declaration of a boolean variable
• var isLoadedBoolean
• //assignmet
• isLoaded true

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Default Values (1/2)

• A Default value is the value that a variable
  contains before you set its value
• You initialize a variable when you set its value
  for the first time
• If you declare a variable, but do not set its
  value, that variable is uninitialized
• The value of an uninitialized variable depends on
  its data type

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Default Values (2/2)

• The following table describes the default values
  of variables, organized by data type
• Note! For variables of type Number, the default
  value is NaN (not a number)

16
Array (1/2)

• Arrays are lists of data under which each item is
  identified by its order within the list
• The first element in an Array has index 0
• An array can be made up of primitive type values
  like strings, numeric values, booleans or complex
  type values like other arrays or objects
• var music_arrayArray new Array()
• music_array "Metallica", "Bruce Springsteen",
  "U2", "Iron Maiden", "David Gray", "Van
  Morrison"
• music_array.length //traces the length of the
  array
• music_array1 //traces Bruce Springsteen
• var my_arrayArray 5,"Hello!",a5, b7
  //complex array

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Array (2/2)

• Example of some methods for the Array object are
• slice, join, concat, push, pop, reverse etc.
• var music_arrayArray new Array()
• music_array "Metallica", "Bruce Springsteen",
  "U2", "Iron Maiden", "David Gray", "Van
  Morrison"
• //slice(startIndex, endIndex)
• music_array.slice(2,4) //traces U2, Iron Maiden

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Typecasting

• Sometimes we need to typecast a data type into
  another (for some reson), for exampe if we load
  XML data (numbers) and Flash interpret it like
  string vaules
• Heres an example of how we can typecast a string
  into a number
• var my_stringString "50"
• var my_numNumber 20
• var answerNumber
• trace(my_string my_num) //traces 5020
• //typecast the string to a number data type
• trace(Number(my_string) my_num) //traces 70

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Scope

• Scope is the realm or space in wich an object
  (variable) lives
• In ActionScript 3.0, variables are always
  assigned the scope of the function or class in
  which they are declared
• Entrance into that scope typically begins a
  variable's lifetime and exit from that scope
  typically ends its lifetime
• function localScope()
• var strLocalString "local"
• localScope()
• trace(strLocal) //error because strLocal is not
  defined globally

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Arithmetic operators

• Arithmetic operators
• , -, , /,
• , - -
• , -, , /,
• Increment , and decrement - -
• Increments/decrements a variable by 1
• var xNumber 10
• x
• trace(x) //traces 11
• x--
• trace(x) //traces 10

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Precedence

• The answer depends on operator precedence
• var iNumber
• i 12 3 10 / 2 //traces 27
• You can override precedence by using parenteses
• var iNumber
• i(12 3) 10 / 2
• trace(i) //traces 75