added section on making decisions
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# The Young Person's Guide to Programming in Minecraft
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## 2013/01/08 17:26
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## Draft
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### Introduction
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Minecraft is an open-ended 3D game where you can build and craft
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@ -839,12 +837,82 @@ logical step. Of course, Minecraft doesn't have the same constraints
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as real-world densely populated areas so let your imagination go wild.
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TODO
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### Making Decisions
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TODO
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#### if then else
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TODO
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All the programs we have seen so far have been fairly predictable - they went
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straight through the statements, and then went back to the beginning again. This is
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not very useful. In practice the computer would be expected to make decisions and
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act accordingly. The javascript statement used for making decisions is `if`.
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While standing on the ground in-game, type the following at the command prompt...
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/js if ( self.flying ) { echo("Hey, You are flying!"); }
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... No message should appear on screen. That is - `Hey, You are
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flying!` should *not* appear on screen. Now double-tap the `space`
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bar to start flying in-game (tap the space bar twice in rapid
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succession), then press and hold space to rise above the ground. Now
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enter the same statement again (If you don't want to type the same
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statement again, just press `/` then press the `UP` cursor key on your
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keyboard, the statement you entered previously should reappear.
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/js if ( self.flying ) { echo("Hey, You are flying!"); }
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... this time the following message should have appeared on your screen...
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Hey, You are flying!
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The `if` statement tests to see if something is `true` or `false` and
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if `true` then the block of code between the curly braces ( `{` and
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`}` ) is executed - but only if the condition is true. The condition
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in the above example is `self.flying` which will be `true` if you are
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currently flying or `false` if you aren't.
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What if you wanted to display a message only if a condition is *not*
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true ? For example to only display a message if the player is *not*
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flying...
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/js if ( ! self.flying ) { echo ("You are not flying."); }
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... This code differs in that now there's a `!` (the exclamation mark)
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before `self.flying`. The `!` symbol negates (returns the opposite of)
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whatever follows it.
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What if you want to display a message in both cases - whether you're
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flying or not? This is where the `if - else` construct comes in handy.
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Open your favorite editor and type the following code into a new file
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in your js-plugins directory...
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function flightStatus()
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{
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if ( self.flying )
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{
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echo( "Hey, You are flying!" );
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}
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else
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{
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echo( "You are not flying." );
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}
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}
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... now type `/reload` at the in-game prompt then type `/js
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flightStatus()` and an appropriate message will appear based on
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whether or not you're currently flying. Type the `/js flightStatus()`
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command while on the ground and while flying. The message displayed in
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each case should be different.
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### Next Steps
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This guide is meant as a gentle introduction to programming and
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modding Minecraft using the Javascript Programming Language.
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Javascript is a very powerful and widely-used programming language and
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there are many more aspects and features. If you want to dive deeper
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into programming and modding minecraft I recommend reading the source
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code to some of the existing scriptcraft add-ons, the *chat* module (
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`js-plugins/chat/chat.js` ) is a good place to start, followed by
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[Anatomy of a ScriptCraft Plug-in][ap]. The online [Craftbukkit API
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Reference][cbapi] provides lots of valuable information about the
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different objects and methods available for use by ScriptCraft.
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[buk]: http://wiki.bukkit.org/Setting_up_a_server
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[dlbuk]: http://dl.bukkit.org/
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[cbapi]: http://jd.bukkit.org/beta/apidocs/
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[boole]: http://en.wikipedia.org/wiki/George_Boole
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[soundapi]: http://jd.bukkit.org/beta/apidocs/org/bukkit/Sound.html
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[ap]: http://walterhiggins.net/blog/ScriptCraft-1-Month-later
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[img_echo_date]: img/ypgpm_echo_date.png
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[img_3d_shapes]: img/ypgpm_3dshapes.jpg
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