How to merge the contents of two variables - actionscript-3

Question

I have many string variables that start with "Question" and then end with a number. ("Question1")
Each variable has a question in it ("How many times does it say E?")
There is an editable textbox on the stage that the user types in which question number he want to be displayed in a different textbox. ("1")
When the user clicks a button, I want that the text of Question1 should be displayed in the textbox.
My code looks like this:
var Question1:String = "How many times does it say E?" ;
var Question2:String = "How many times does it say B?" ;
var Question3:String = "How many times does it say A?" ;
myButton.addEventListener(MouseEvent.CLICK, displayQuestion);
function displayQuestion(event:MouseEvent):void
{
var QuestionNumber:Number = Number(userInputQuestionNumber.text);
textBoxDisplayQuestion.text= Question(QuestionNumber);
}
How can I get the textBoxDisplayQuestion to display the actual text of the Question??
(the code i have now obviously is not working!!)
But this example doesnt seem to work: I created a class called Question and here is the code:
import Question;
var QuNoLoad:Number;
var Qu1:Question = new Question(1,"how","yes","no","maybe","so","AnsB","AnsA");
trace(Qu1.QuNo, Qu1.Qu, Qu1.AnsA,Qu1.AnsB, Qu1.AnsC, Qu1.AnsD, Qu1.CorAns, Qu1.FaCorAns);
//the following is the code for the button
loadQu.addEventListener(MouseEvent.CLICK, loadQuClick);
function loadQuClick(event:MouseEvent):void
{
//this sets the variable "QuNoLoad" with the contents of the "textBoxQuLoad"
//imagine the user inputed "1"
QuNoLoad=Number(textBoxQuLoad.text);
//this SHOULD!! display the contents of "Qu1.Qu"
textQu.text= this["Qu"+QuNoLoad.toString()+".Qu"]
//and when i traced this statment the value was "undefined"
}
Why???

Answer 1

You can reference a variable by name using square brackets [] operator, such as:
this["Question" + QuestionNumber.toString()]
You may use this operator to dynamically set and retrieve values for a property of an object.
Keeping the question number as an integer, your function would be:
var Question1:String = "How many times does it say E?" ;
var Question2:String = "How many times does it say B?" ;
var Question3:String = "How many times does it say A?" ;
function displayQuestion(event:MouseEvent):void
{
var QuestionNumber:uint = uint(userInputQuestionNumber.text);
textBoxDisplayQuestion.text = this["Question" + QuestionNumber.toString()];
}

Answer 2

This is a pretty fundamental concept in programming that will make a lot of things harder to do until you understand it well, and it's pretty hard to explain without starting with some groundwork:
What's happening here is easiest to talk about with plain old Object rather than classes, so lets start with a very simple example:
var question1:Object = new Object();
question1.number = 1;
Note that with Object you didn't have to say that number existed ahead of time, it gets created when you set it. Now, when you say either question1.number you get 1, obviously. What is happening, however is that first question1 gets the value you stored in the variable question1 (which is { number: 1 }), then the .number gets the value stored in the property number stored in that value: 1.
To save some typing, you can use a shorthand called "object literals":
var question1 = {
number: 1
};
Now lets try a more complex object:
var question1 = {
number: 1,
text: "How many times does it say A?",
answers: {
a: 1,
b: 2,
c: 3,
d: 4,
correct: "b"
}
};
Now question1 is an object that has 3 properties, one of which, answers, is an object with 5 properties: a, b, c, d, and correct. This could also be written as:
var question1 = new Object();
question1.number = 1;
question1.text = "How many times does it say A?";
question1.answers = new Object();
question1.answers.a = 1;
question1.answers.b = 2;
question1.answers.c = 3;
question1.answers.d = 4;
question1.answers.correct = "b";
It should be pretty clear why the literal syntax exists now!
This time, if you say question1.answers.correct you get "b": first question1 gets you the { number: 1,...} value, then the .answers gets the { a: 1, b: 2,...} value, then finally the .correct gets the "b" value.
You should also know that this is a special variable that has a particular meaning in ActionScript (and JavaScript, on which it is based): it broadly refers to the object in when the code you are writing is inside: for "global" code (not inside a function), var adds properties to this object: var number = 2; and this.number = 2 are this same here. (This is not true when you're in function, this behaves differently there, sometimes in very strange ways, so be careful!)
Now you might start seeing what's happening: when you use [], for example, question1["number"], rather than question1.number, you are passing the property name you want to get as a String value, which means you can change what property you get while you are running, rather than when you compile ("runtime" vs. "compiletime"), but it also lets you get properties with names you can't refer to with the . syntax!
var strange = {
"a strange name? That's OK!": 1
};
trace(strange["a strange name? That's OK!"]);
So when you write this["Qu" + QuNoLoad.toString() + ".QuNo"], you create a name like "Qu2.QuNo", for example, you are trying to get a property with that exact name, . included, which doesn't exist! What you were trying to do the equivalent of: Qu2.QuNo could be written as this["Qu" + QuNoLoad].QuNo.
I shouldn't leave this without saying, though, that for something like this, I would use arrays, which exist so that you can use a single name to store a list of values:
var questions:Array = [ // set questions to an array with multiple questions
new Question(...),
new Question(...),
...
];
for each (var question:Question in questions) { // Look at each question in the array
if (question.QuNo == textBoxQuLoad.text) { // If this is the right question
loadQuestion(question);
break; // Found it, stop looking at each question by "breaking out" of the for each
}
}
There's lots more you can do with arrays, so read up on them when you get time.