Transcript For - loop - Interaction Design Umeå

Introduction to
Flash ActionScript 3.0
Statements & Loops
Thomas Lövgren, Flash developer
[email protected]
Conditional Statements
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A way for the computer to make a choice based on some condition
”If it is dark, then light the lamp, if not, leave it off.”
The operator checks a specific condition for the statement(s)
The condition could be either true or false depending on the setup
The if - statement is the most important conditional statement in
ActionScript
if (statement_one operator statement_two){
//run code
}
If & else statement
Example of a if-statement with the operator ">"
(If var1 is greater than var2)
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if(x > 100){ //statement
trace("X is too big"); //output
}
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Instead of writing another if-statement you can use the elsestatement to catch when the condition evaluates to false
if(x > 100){
trace("X is too big");
}else{
trace("X is not too big");
}
Operators
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Relational and Equality operators, evaluates to true or false
Operator Function/task
==
>=
>
<=
<
!=
&&
||
If
If
If
If
If
If
If
If
var1 is equal to var2
var1 is greater than or equal to var2
var1 is greater than var2
var1 is smaller than or equal to var2
var1 is smaller than var2
var1 is NOT equal to var2
var1 and var2 exist or both var1 and var2 are both set to true
either var1 and var2 exist and/or are set to true
Statements examples (1/2)
if(hungry && !thirsty){
trace("go get a combo from the closest burger joint");
}
if((variable_1 == variable_2) && (variable_3 > variable_4)){
trace("variable 1 is equal to variable 2 and variable 3 is greater
than variable 4");
}
if(theTimeOfDay == theMorning){
trace("wake up");
} else if(theTimeOfDay == myBedTime){
trace("go to bed");
} else if(iShouldBeAtWork){
trace("working right now");
} else {
trace("watch some tv");
}
Statements examples (2/2)
//declare variables and assign values
var videoLoaded:Boolean = false;
var getData:Boolean = false;
//if statement
if(videoLoaded){ //is videoLoaded true?
trace("The video is loaded"); //will not execute
}
if(!getData){ //is getData false?
trace("The getData variable is false"); //will execute
}
Switch Statement
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Switch Staements are useful when you want to respond to a series
of possible values that a variable might have (instead of writing
long If-structures)
var switchExpression:int = 3; //declare variable
switch(switchExpression){ //switch statement
case 0:
trace(0);
break;
case 1:
trace(1);
break;
case 2:
trace(2);
break;
default:
trace("not case 0, 1, or 2"); //traces not case 0, 1, or 2
}
Loops
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ActionScript loops are used to execute a segment of code
repeatedly for a number of times or while a certain condition is
satisfied
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This can save time and effort by not having to type the same code
multiple times to repeat a process
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Example of loops:
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For - loop
While - loop
Do/While loop
Loops
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Flowchart example of a loop
For - loop
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The for-loop is probably the most commonly used because it is the
most compact and the easiest to understand and use
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Structure
for (counter; condition; action){
statements;
}
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Example
for (var i:int = 0; i < 10; i++){ //for-loop
trace ("This code is repeated ten times"); //output
}
While - loop
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The While - loop repeats a set of code as long as the condition
specified is true
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Structure
while (condition) {
statements
}
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Example
var i:int = 1;
while (i < 5){ //condition
trace ("This code is repeated"); //output
i++; //increase counter
}
Do - While loop
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A Do While loop will take a comparison statement and as long as
the statement returns true, the loop will run
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Structure
do {
statements;
} while (condition);
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Example
var i:int = 1;
do {
trace ("This code is repeated"); //output
i++; //increase counter
}while(i < 5); //condition
Reverse Loop & statement
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It’s also posible to count down by reversing the values, and then
decrementing the counter
//reverse loop
for (var i:int = 10; i > 0; i--){
trace("Hello: " + i); //output
}
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Example of an If-statement inside a for-loop:
for (var i:int = 0; i < 100; i++){ //for-loop
if(i > 50){ //if-statement
trace(i + ": is greater than 50"); //output
}
}
Array & Loops
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Loops are very often used to manipulate and access the content of
arrays
var movie_array = new Array();
movie_array = ["Batman", "The Godfather", "Star Wars", "Lord of
The Rings", "Titanic"];
//loop through the array
for (var i:int = 0; i < movie_array.length; i++){
trace (movie_array[i]); //output
}
/* Batman
The Godfather
Star Wars
Lord of The Rings
*/ Titanic
String & Loops
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We can use a loop to go through a text string, and for example
replace a word or a specific character
//declare string and assign value
var book_string:String = "IT by Stephen King";
for (var i:int = 0; i < book_string.length; i++){
trace("Character " + i + ": " + book_string.charAt(i));
}
/* output
Character
Character
Character
Character
……
*/
0: I
1: T
2:
3: b
Named Loops
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By naming a loop when you call break you can target the named
loop as the break. This example shows a Nested for-loop:
//my top loop
outsideLoop:for(var i:int = 0; i < 10; i++){
trace(i + ": called from outsideLoop"); //output
//my inside loop
insideLoop:for(var j:int = 0; j < 5; j++){
trace(j + ": called from insideLoop");
if(j < 2) break outsideLoop; //stop the outside loop
}
}
New Loops in AS3
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Examples of the new loop construct in AS3:
//set up the array
var my_array:Array = ["test", "test2", "test3"];
//use a regular for in loop to access the properties in my_array
for (var element:String in my_array){
trace(my_array[element]); //traces test, test2, test3
}
//use the new for each in loop to access the values in my_array
for each (var indexData:String in my_array){
trace(indexData); //traces test, test2, test3
}