Flash MX 2004 Games : Art to ActionScript

11 Debugging
No matter how experienced you get at writing code, there will be times when the code you
write doesn’t work the way you expect. Isolating and fixing the errors is called debugging and is
a fascinating mental challenge, or a complete headache depending on how you are feeling that
day! In this chapter we will look at many of the more common errors and look at techniques for
isolating the problem and then fixing it.
Strings and numbers
You have created a game that allows the user to input a numeric value using an input box. Then
you run this code:
on (release){
num = num + userInput;
}
You have a num of 14, and a userInput of 10. You expect the num to be set to 24; instead it is set to
1410. Why? Simple really, userInput is a string; all input boxes store data as a string. The operation
‘+’ can be applied to strings, so Flash converts num, 14, into the string ‘14’ and ‘adds’ it to the
string ‘10’. The string operation ‘+’ is concatenation, the string to the left of the operator and the
string to the right are joined together. This is not the method that was intended; in your code you
wanted the string ‘10’ to be used as a number. One solution is to make sure Flash realizes to use
userInput as a number by using the ‘Number’ method:
on (release){
num = num + Number(userInput);
}
The result will now be a number, 24, as you intended. If the combination operation were any
other arithmetic operation then Flash would have realized that you intended to use userInput as a
numeric quantity, because no other arithmetic operation applies to strings. Therefore:
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on (release){
num = num - userInput;
}