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Tutorials » Actionscripting/Basic

Flash Actionscript Programming Basics
Author: Steve Happ | Website: http://www.video-animation.com |

Arithmetic "IF" operator

The syntactic form is:
Expression1 ? expr2 : expr3 ;
If expression1 evaluates to a true condition, then expression2 is evaluated, otherwise expression3 is evaluated. E.g.

x = 2;
y = 5;
max = x


Bitwise Operators

Bitwise operators operate on the value to base 2 (binary). Operands must be integers.


Left Shift ("<<") - shifts the bits of the left operand some number of positions to the left.
e.g. 

someNum = 1;
0 0	0 0	0 0 0 1
SomeNum = someNum<<1;
0 0 0 0 0 0 1 0
SomeNum = someNum<<2;
0 0 0 0 1 0 0 0
Right Shift (">>")
SomeNum = someNum>>3;
0 0 0 0 0 0 0 1

The leftShift operator inserts "0" from the right.

The Right Shift operator inserts "0" from the left.



Variables (AS 2.0)

A variable is identified by a user-supplied name. Each variable is of a particular data type. E.g.

Var num:Number;

"Number" is a type specifier. A declaration can follow the template:
var variableName:DataType;


The use of the ":Datatype" is not strictly enforced in AS2 but I strongly recommend it.

A variable can be composed of letters, numbers and underscore. Upper and lower case letters are different.

Variables need to be initialised. I.e. given an initial value.

var myNum:Number;	//Declaration
myNum = 0;		//Initialisation


In AS 1.0, variables are not strictly typed and can change types.



DataTypes (AS 2.0 only)

Variables in AS 2.0 can be given strict datatypes such as a Number or a String or a Boolean.
e.g.

var myNum:Number;
var myString:String;
var isTested:Boolean;

In AS 1.0 there is no strict datatyping. A number can become a String and vice versa.
e.g. 

num = 10;
num = "Test";

Strict datatyping can capture errors.


Compiler Errrors

	Syntax errors  - e.g. var numberOne:
	Spelling Mistakes - var mc:MoveiClip;
	DataType Errors - (AS 2.0)


var num1:Number;
var str1:String;
num1 = "Steve";
str1 = 27;



Flow control

IF

An if statement tests a condition. If it is true, then a set of actions is executed.
Otherwise, the set is ignored or bypassed. Here is a template : 

 If(expression){
 Statement1;
 }

Here is an example :
 var x = 23;
 if(x>3){
 trace("x is greater than 3");
 }



IF .. ELSE

If .. else allows for a kind of either .. or condition. 

Template: 

If(expression){
 Statement1;
 }else{
 statement2;
 }

If expression is true then statement1 is executed. 

If expression is false then statement2 is executed.

e.g.
var x = 2;
if(x> 3){
trace("condition is true");
}else{
trace("condition is false");
}



Switch (AS 2.0 only)

A switch statement is an alternative to complex nested if .. else statements
switch(variable){
 case 1:
 //Statement1;
 break;
 case 2:
 //Statement2
 break;
 default:
 //statement3;
 break;
 }

The variable to be evaluated is inserted into the switch argument.
If the first variable's value is 1 then statement1 is evaluated.
A break statement is inserted after it so that the switch statement is terminated.
The default label is the condition for "everything else".

var tester:Number;
tester = random(3);
switch (tester) {
case 1 :
 trace("tester = 1");
 break;
case 2 :
 trace("tester = 2");
 break;
case 3 :
 trace("tester = 3");
 break;
default :
 trace("Out of range");
 break;
}








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Added: : 2005-08-10

Rating: 8.17 Votes: 12

Hits: 670





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 Steve Happ is the founder of Steve's Tutes and has been going hard at it developing Flash for Web and CD-rom.



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