Macromedia Flash Professional 8 UNLEASHED [Electronic resources] نسخه متنی

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.