Flash MX 2004 Games : Art to ActionScript

Chapter 11: Debugging
would give the result 4, if num was 14 and userInput was 10, with no requirement to force userInput
to be a number. Flash ‘knows’ that if you are using the ‘–’ operator then the value to the left and
right of the operation is a number.
In many languages you are forced to define what type of variable you are using, then when
you combine incompatible types you are warned. Flash up to MX 2004 was not a strongly typed
language so you have to be careful that you are combining data types in the way intended. Now
that strict data typing is available you are recommended to use it.
Declare your variables
Flash does not force you to declare variables. This is both a benefit and a problem. See if you can
work out what will happen in the following code:
piece = 10;
trace("The current value of piece is " + getPiece());
function getPiece(){
return peice;
}
Award yourself a prize if you thought that the value returned would be undefined. Instead of 10
being the return value, the value will be empty because there is a typo error. The function returns
the value of the undefined variable ‘peice’ instead of the variable ‘piece’.
Errors like this are quite hard to spot because Flash creates variables as you use them. In a strongly
typed language you would get a compilation error because you are returning a value that does not
exist.
Here’s another one:
1 i=10;
2 trace(sumUpTo());
3 i--;
4 trace(sumUpTo());
5
6 function sumUpTo(){
7 total = 0;
8 while (i>0){
9 total += i;
10 i--;
11 }
12 return total;
13 }
Listing 11.1 ‘Examples/Chapter11/debug03.fla’
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