Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
A special kind of number
If you use
1 var ready:Boolean = false;
2 var x:Number = 10;
3 trace(ready);
4 ready = x>5;
5 trace(ready);
Listing 7.3
Here we use a special kind of number, a Boolean.
Booleans are named after George Boole who was born in Lincoln, England, on 2 November 1815. In
1854, he published his greatest and most influential work, An Investigation into the Laws of Thought, on
Which are Founded the Mathematical Theories of Logic and Probabilities, in which he brilliantly combined
algebra with logic, the foundation of today’s digital computers.
A Boolean can have only one of two values: it is either true or false. In the short Listing 7.3 we
first set the Boolean variable ‘ready’ to false. Then we set a variable x to the value 10. In line 3
we trace the value of ‘ready’ to the Output window. At this stage the variable has the value ‘false’.
Then we assign to ‘ready’ the value (x > 5). This reads as x is greater than 5. Clearly 10 is greater
than 5 so the statement is true. When we again trace ‘ready’ in line 5 it now has the value true.
Booleans are used extensively in game logic and we will meet them many times in this book.
Creating and using string variables
A third kind of variable is a string variable. A string is simply a sequence of characters. ActionScript
contains lots of useful methods for combining and accessing the characters in a string. You can
create a variable that describes someone’s name:
var name:String = "Steve";
Or you can create a variable that can store a sentence:
var saying:String = "The early bird catches the worm";
‘Example/Chapter07/Variables04.fla’ shows how you can use several of the methods of the string
object. Listing 7.4 shows the code:
1 var person:String = "Steve";
2 var desc:String = "The winner is ";
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