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<div class="moz-cite-prefix">On 6/4/2014 9:19 AM, JOHNSON JULIE M.
wrote:<br>
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<p class="MsoNormal">How do you create and use a global variable
in Alice 3.1?<o:p></o:p></p>
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<fieldset class="mimeAttachmentHeader">Global variables are
discouraged by most software engineers, due to unwanted
side-effects that may occur when multiple programmers are
working on the same software application. However, there are
some cases in which a global variable is handy. One example is
in a game program where you are tracking things like score,
time, and end-of-game conditions. These conditions often need to
be checked and/or updated in several different methods. Alice 3
takes a "middle-of-the-road" stance on this issue. On the one
hand, Alice 3 discourages global variables by declaring
variables as (1) local to a specific method, or (2) private to a
specific class. However, the Scene class is (in a sense) global
in that all the objects are located all the action takes place
in a scene. You can take advantage of this by creating a
property variable in the Scene class. This variable is then
"global" to all procedures and functions defined in the Scene
class. As an example, in the first screen capture below, a
property variable is declared in the Scene class to track the <i>score</i>
of a game. In the second screen capture below, the updateScore
procedural method increases the score by 2. We could also write
other methods that access the score... for whatever purpose.<br>
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<img alt="declare score variable"
src="cid:part1.04030502.01050707@andrew.cmu.edu" height="472"
width="358"><br>
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<img alt="update the score"
src="cid:part2.03020902.09000109@andrew.cmu.edu" height="119"
width="398"><br>
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cite="mid:cfb53094773643ad863b689902c45842@EXCAS2.williamsvillek12.net"
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