Statements & Loops

Introduction to Flash ActionScript 3.0 Statements & Loops Thomas Lövgren, Flash developer thomas.lovgren@humlab.umu.se

Conditional Statements • 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) if(x > 100){ //statement trace("X is too big"); //output } • Instead of writing another if-statement you can use the else- statement to catch when the condition evaluates to false if(x > 100){ trace("X is too big"); }else{ trace("X is not too big"); }

Operators • Relational and Equality operators, evaluates to true or false Operator Function/task == If var1 is equal to var2 >= If var1 is greater than or equal to var2 > If var1 is greater than var2 <= If var1 is smaller than or equal to var2 < If var1 is smaller than var2 != If var1 is NOT equal to var2 && If var1 and var2 exist or both var1 and var2 are both set to true || If 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 varvideoLoaded:Boolean = false; vargetData: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 • 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) varswitchExpression: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 • ActionScript loops are used to execute a segment of code repeatedly for a number of times or while a certain condition is satisfied • This can save time and effort by not having to type the same code multiple times to repeat a process • Example of loops: • For - loop • While - loop • Do/While loop

Loops • Flowchart example of a loop

For - loop • The for-loop is probably the most commonly used because it is the most compact and the easiest to understand and use • Structure for (counter; condition; action){ statements; } • Example for (var i:int = 0; i < 10; i++){ //for-loop trace ("This code is repeated ten times"); //output }

While - loop • The While - loop repeats a set of code as long as the condition specified is true • Structure while (condition) { statements } • Example var i:int = 1; while (i < 5){ //condition trace ("This code is repeated"); //output i++; //increase counter }

Do - While loop • A Do While loop will take a comparison statement and as long as the statement returns true, the loop will run • Structure do { statements; } while (condition); • Example var i:int = 1; do { trace ("This code is repeated"); //output i++; //increase counter }while(i < 5); //condition

Reverse Loop & statement • 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 } • 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 • Loops are very often used to manipulate and access the content of arrays varmovie_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 • 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 varbook_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 0: I Character 1: T Character 2: Character 3: b …… */

Named Loops • 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 • Examples of the new loop construct in AS3: //set up the array varmy_array:Array = ["test", "test2", "test3"]; //use a regular for in loop to access the properties in my_array for (varelement: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 (varindexData:String in my_array){ trace(indexData); //traces test, test2, test3 }

Statements & Loops