Flash MX 2004 Games : Art to ActionScript

Chapter 1: Your first game
is true or not. Flash lets you store all this information. A variable takes a name, which can be any
name that you find useful. In this instance I chose the name ‘keypressed’ and I have set this to
false. So at this stage in this section of code the variable ‘keypressed’ is false.
Then we move on to use a most important tool in the programmer’s armoury, the ‘if’ statement.
The syntax of an ‘if’ statement is
if (test){
//Do this if test is true
}else{
//Do this if test is false
}
The standard brackets contain the test. What could we use here? It can be anything that evaluates
to true or false. In Chapter 8 we will look in detail at how to use the ‘if’ statement but for now just
remember true or false. If something is true then do whatever is in the first set of curly brackets. If
it is false then do whatever is in curly brackets following the optional ‘else’ statement.
We are using the clip event to move the bat up or down. It will move up if the ‘K’ key is
pressed and down if the ‘M’ key is pressed. In Flash we can test whether a key is pressed using
Key.isDown(75)
The number in the brackets selects the key; you will learn how to find out a key’s number later in
the section on debugging. If the key is down then the result is true, if the key is not down then the
result is false. In the ‘if’ statement test we look for two things, one is the whether a key is down
and the other is the value of ‘_y’. This value is stores the position up and down the screen of the
movie clip itself. To avoid it going too high we want to make sure that this value is always greater
than 50. We can combine these two tests by using the operator ‘&&’. Now both the tests must
be true for the combination of the tests to evaluate to true. This is called logical ‘And’. Again later
we will look into combining logical operations, for now just accept that the test decides whether
the K key is pressed and whether the movie clip is not too high up the screen. If all this is true
then we move on to the code within the curly brackets.
if (moveY>=0){
moveY = -1;
}else if (moveY>-15){
moveY *= 1.2;
}
keypressed = true;
_y += moveY;
What, another ‘if’ statement? Yes, programming often involves the use of many conditions.
Here we know that the user is pressing the K key and that the bat is not yet in the top position.
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