Chapter11.Statements and Expressions

Chapter 11. Statements and Expressions

IN THIS CHAPTER

• Statement Syntax

• Object Statements

• Flow Modifiers

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.