This chapter covers statements and expressions. Even though we have not formally gone over statements, you have already used them. A statement is simply a small piece of code made up of keywords, operators, and identifiers. Statements can be in one of six categories:
Declaration statements These statements involve declaring variables, creating functions, setting properties, declaring arrays, and so on. Here's an example:
var myVariable:String; // declares a variable myObject._x = 235; //setting the horizontal position var my_array:Array = new Array ();//creating an array function myFunction (){ //creates a function
Expressions These include any type of legal expression. Here's an example:
i++; //increase a variable lName + space + fName; //combining variables
Flow modifiers These include any statement that disrupts the natural flow of the interpreter reading the ActionScript. There are two subtypes of flow modifiers: conditional statements and loop statements.
Conditional statements use Boolean answers to determine what to do next or what not to do next. Here's an example:
if (inputName == userName){ if (inputPassword == password){ gotoAndPlay("startPage"); }else { displayMessage = "Double check your password"; } }else if (inputName != userName){ if (inputPassword == password){ displayMessage = "Double check your user name"; } }else{ displayMessage = "Double check your all your information"; }
Loop statements run until a defined condition has been met. Here's an example where the trace function will be run while i is less than 30:
for (var i:Number=0; i<30; i++) { trace (i); } //output: (numbers 0-29)
Predefined functions Functions that are predefined in ActionScript. Here's an example:
trace ("function"); //a simple trace function gotoAndStop (2); //a playback function getProperty( myMovie, _x ); //gets the horizontal position
Object statements Statements that deal with and manipulate objects. Here's an example:
var myGrades:Object = { tests: 85, quizzes: 88, homework: 72 }; for (name in myGrades) { trace ("myGrades." + name + " = " + myGrades[name]); } //output: myGrades.tests = 85 // myGrades.quizzes = 88 // myGrades.homework = 72
Comments This last category is one of a kind. It includes comments used in code merely as information for the user while in the Actions panel. The interpreter will skip over these comments. Here's an example:
//this is a comment used in ActionScript; /*this is a comment block */
Breaking up statements into these simple categories is done only to help you understand the different types and uses of statements. We will go over a few of these categories in more detail later in this chapter.
Now let's look at some of the basics of building these statements.