scriptcraft/docs/YoungPersonsGuideToProgrammingMinecraft-de.md

# The Young Person's Guide to Programming in Minecraft

## Einführung

Minecraft ist ein 3D Spiel ohne festes Spielziel. Mit einfachen Blöcken kannst
du ganze Welten bauen oder auf Entdeckungsreise durch eine immer weiter
generierte Welt gehen. Minecraft kann mit Hilfe von 'Mods' (Kurzform für
modifications) -- also mit weiterem Programmcode -- erweitert werden.
ScriptCraft ist eine solche Modifikation, die es dir erlaubt, direkt im Spiel
JavaScript zu benutzen. Damit sind folgende Dinge möglich:

 * Mit simplen JavaScript Befehlen Blöcke bauen
 * Das Spiel mit interessanten neuen Eigenschaften ausstatten (neue
   Items hinzufügen, das Spielverhalten beeinflussen und Mini-Games
   erstellen)

Du kannst Minecraft im Einspieler- und im Mehrspielermodus mit Freunden
spielen. Die meisten spielen Minecraft im Multiplayermodus online über das
Internet oder lokal.

![Cottages created using ScriptCraft in MineCraft][img_cr]

## Installation

CraftBukkit ist eine spezielle Server-Version von Minecraft, die es dir auf
einfache Weise erlaubt, Modifikationen und Erweiterungen für Minecraft zu
erstellen. ScriptCraft ist eine solche Modifikation, die CraftBukkit benutzt.
Modifikationen für Minecraft zu erstellen ist schwer, ScriptCraft macht dies
dir einfacher. Folgende Schritte sind zur Installation notwendig:

1. [CraftBukkit herunterladen und installieren][dlbuk].

2. Die [ScriptCraft Modifikation herunterladen][sc-plugin]. Danach in das
   Verzeichnis `craftbukkit/plugins` kopieren, das im ersten Schritt erstellt
   wurde.

3. Den CraftBukkit Server starten.

4. Operator-Berechtigung setzen. Dazu musst du im CraftBukkit Consolenfenster
   `op {username}` eingaben und mit ENTER bestätigen (`{username}` natürlich
   mit dem eigenen Minecraft Spielernamen ersetzen). Dieser Befehl sorgt dafür,
   dass diesem Spieler Administratorrechte gegeben wird. Damit kannst du
   weitaus mehr Befehle auf dem Server ausführen als ein normaler Spieler.

5. Um sicherzustellen, dass die Installation funktioniert hat und alles richtig
   eingerichtet ist, kannst du im CraftBukkit Consolenfenster `js 1+1`
   eingegeben. Es sollte nun `> 2` erscheinen.

Gratulation! Jetzt ist alles bereit um mit dem Programmieren in ScriptCraft zu
beginnen. Normalerweise werden Modifikationen in Java programmiert. Dies macht
das Erstellen von eigenenen Modifikationen oder neuer Spiellogik schwer, da du
zuerst Java lernen musst. Mit dem ScriptCraft Plugin ist es nicht mehr nötig
Java programmieren, du kannst stattdessen JavaScript verwenden. JavaScript ist
einfacher zu lernen als Java und ist zugleich flexibler. JavaScript kannst du
auch für die Erstellung von dynamischen Webseiten oder gar Server-Anwendungen
verwenden.

## JavaScript lernen

Da du coole Sachen in Minecraft mit ScriptCraft machen willst, *musst* du nicht
viel von JavaScript wissen. Es genügen schon ein paar Grundlagen, damit du mit
der Programmierung beginnen kannst. Du musst dir deshalb keine Sorgen machen,
dass du am Anfang noch nicht alles kennst, das kommt mit der Zeit automatisch.
ScriptCraft bringt eine Menge Funktionen mit, um Formen und Objekte zu bauen.
Je mehr man sich mit JavaScript auskennt, desto mehr kann man auch machen --
nicht nur einfache Formen und Gebäude, sondern auch neue Spielregeln, Items,
Aktionen, sogar kleine Multiplayerspiele. Für JavaScript-Grundlagen empfehle
ich dir das [lustige JavaScript Tutorial][ce], für den direkten Einstieg in
ScriptCraft, einfach hier weiterlesen ...

### Erste Schritte

Keine Sorge, wenn du noch nie etwas mit JavaScript gemacht hast. Du wirst im Verlauf
dieses Textes einiges über JavaScript und dem Programmieren im Allgemeinen lernen.
Der Minecraft Server ist aufgesetzt, bereit zu verbinden ...

1. Starte Minecraft (lasse das Bukkit Befehlsfenster offen)
2. Klicke auf "Multiplayer" und dann auf "Add Server"
3. Die Serveradresse ist "localhost". Dies ist ein spezieller Hostname, welcher
   auf den eigenen Computer verweist.
4. Klicke auf "Join Server" um auf den Bukkit Server zu verbinden.
5. Nach dem du dem Spiel beigetreten bist, kannst du mit der `/`-Taste das
   Chatfenster öffnen. Eine Eingabezeile erscheint, in das du NAchrichten, aber
   auch Befehle eingeben kannst. Probiere `js 1+1` aus, die Nummer 2 sollte
   erscheinen.

Sehr gut! Du hast eben JavaScript Code eingegeben, welcher vom ScriptCraft
Plugin interpretiert wurde und das Ergebnis direkt im Spiel angezeigt wurde.

### Variablen

Mit einer Variable kannst du (der Programmierer) Dingen einen Namen geben. In
JavaScript werden Variablen mit dem `var` Schlüsselwort erstellt.

    /js var position = "Saurons Festung"

Dies erstellt eine neue Variable mit dem Namen `position`, welche den Text
"Saurons Festung" enthält. Ab jetzt hat der Computer einen neuen Eintrag
im Speicher mit dem Namen `position`. Diesen Namen können wir so nutzen ...

    /js echo(position)

... um folgendes anzuzeigen:

    Saurons Festung

Du wunderst sich vermutlich, wo die `""` abgeblieben sind. Um Text in einer
Variable zu speichern, muss dieser in `"` eingeschlossen werden. Der Computer
speichert die doppelten Anführungszeichen dabei aber nicht mit, nur den
eigentlichen Text. Variablen werden im Minecraft Server gespeichert, während
dieser läuft. Wiederhole den letzten Befehl den du eingegeben hast (drücke dazu
`/` und danach `Pfeil nach oben`). Du kannst den Befehl so oft wiederholen
wie du willst, der Computer wird jedes Mal den selben Wert ausgeben. Du kannst
diesen Wert auch ändern:

    /js position = "Das Auenland"

Beachte hierbei, dass das `var` Schlüsselwort fehlt, es wird nicht mehr
benötigt. Das `var` Schlüsselwort muss nur bei der Erstellung mit angegeben
werden. Jetzt führe folgenden Befehl aus:

    /js echo(position)

... und es erscheint:

    Das Auenland

Variablen können in JavaScript einfach angelegt und verändert werden. Neben
Variablen die du dir selbst anlegst gibt es auch Variablen, die ScriptCraft
für dich bereits angelegt hat. Eine solche Variable ist `self`. Diese
enthält Informationen über den aktuellen Spieler:

    /js echo (self)

Folgendes erscheint:

    CraftPlayer{name=fu86}

Natürlich ist der ausgegebene Name bei jedem Spieler ein anderer. Bei dir sollte
dein Name erscheinen.

### Funktionen

ScriptCraft bringt ein paar Funktionen mit, die im normalen JavaScript
nicht zu finden sind. Diese Funktionen helfen dir, neue Strukturen
und Gebäude zu erstellen, für die du normalerweise händisch Stunden
brauchen würdest. Bevor wir allerdings die Bau-Funktionen näher
betrachten, schauen wir uns die `echo()` Funktion an.

Die `echo()`-Funktion -- wie der Name schon vermuten lässt -- gibt alles zurück, was
du ihr als Parameter übergibst. Hier ein Beispiel:

    /js echo("Hallo")

... und im Spiel wird folgendes erscheinen:

    Hallo

... tippe ...

    /js echo(5+7)

... und im Spiel wird folgendes angezeigt:

    12

Damit kannst du sogar in Minecraft rechnen und deine Mathe-Hausaufgaben machen,
was aber nicht zu empfehlen ist. Hausaufgaben und Minecraft passen nicht sehr
gut zusammen! Die `echo()`-Funktion gibt alles aus, was sie als Parameter
bekommt; Text, Nummern und ganze Ausdrücke. Ein weiteres Beispiel:

    /js echo(new Date())

... gibt das aktuelle Datum aus. Wenn der Ausdruck oben für dich verwirrend
erscheint, mach dir keine Sorgen; `new Date()` erstellt ein neues
`Date`-Objekt, was das ist, wird später noch erklärt.


    Tue Jan 08 2013 20:53:37 GMT-0000 (GMT)

![Das heutige Datum][img_echo_date]

`echo()` ist eine sehr nützliches Funktion, sie ist aber nicht Teil der
JavaScript Programmiersprache. Du kannst sie nicht ausserhalb von Minecraft
verwenden. Es gibt aber Funktionen, die in JavaScript enthalten sind, die auch
in ScriptCraft verwendet werden kann. Ein Beispiel:

    /js Math.max(6, 11)

... gibt die größere der beiden Zahlen zurück (max ist das Kürzel für Maximum).
Mit dieser Funktion ...

    /js Math.min(6, 11)

... kann man dagegen die kleinere der beiden Zahlen zurückgeben. In JavaScript
hat jeder Ausdruck einen Rückgabewert. Das unterscheidet JavaScript von
Sprachen wie PHP oder C. Wenn das für dich im Moment keinen Sinn ergibt, ist
das nicht schlimm, es wird rgend wann plötzlich Sinn ergeben. Das Ergebnis
eines beliebigen Ausdrucks lässt sich in einer Variablen speichern. Etwa
so:

    /js var groesser = Math.max(6, 11)

Das Ergebnis steckt nun in der Variable `groesser`.

    /js groesser

Dieses Mal haben wir nicht die `echo()`-Funktion verwendet, aber es wurde
trotzdem 11 zurückgegeben. ScriptCraft gibt immer den Rückgabewert auf
der Minecraft Console aus.

Du kannst allerdings auch eigene funktionen schreiben:

    /js function aktuelle_uhrzeit() { return new Date() }

Hier hast du eben eine neue Funktion mit dem Name `aktuelle_uhrzeit` angelegt,
die jedes Mal ein neues `Date`-Objekt zurückgiebt, wenn sie aufgerufen wird. Du
hast vielleicht gemerkt, dass der Aufruf oben keinerlei Effekt hatte und nichts
passiert ist -- nicht mal die aktuelle Uhrzeit wurde ausgegeben. Das liegt daran,
dass der Inhalt der Funktion erst verarbeitet wird, wenn die Funktion aufgerufen
wird. Also rufen wir die Funktion auf:

    /js aktuelle_uhrzeit()

... und die aktuelle Uhrzeit erscheint im Spiel. Gratulation, du hast soeben
deine erste JavaScript-Funktion geschrieben. Du bist auf dem richtigen weg,
ein Minecraft Modder zu werden :-)

Es gibt eine Menge fertiger Funktionen, die du nutzen kannst. Zum Beispiel
folgende:

    /js Math.random()

... diese gibt jedes Mal eine zufällige Nummer aus, wenn du sie aufrufst. Probier
es aus! Führe die Funktion ein paar mal aus (mit der Pfeil nach oben Taste geht
das schneller) und es wird jedes Mal eine neue Zufallszahl ausgegeben. Du kannst
dir `Math.random()` wie ein Würfel mit sehr vielen Seiten vorstellen. Jedes Mal
wenn du die Funktion aufrufst, wird erneut gewürfelt.

## Dinge in Minecraft bauen

Jetzt kommen wir zum interessanten Teil -- Objekte und Gebäude in Minecraft
bauen. Von Hand bauen macht Spaß, doch wird anstrengend wenn man große und
aufwändige Dinge wie Türme, Burgen oder ganze Festungen bauen will. Hier kommt
ScriptCraft ins Spiel. ScriptCraft besitzt ein paar JavaScript-Funktionen, die
kombiniert viele interessante Dinge hervorbringen können. Fangen wir einfach an
um ein Gefühl dafür zu bekommen, wie ScriptCraft's Baufunktionen funktionieren.
Die Funktion, die du vermutlich am meisten verwenden wirst ist die
`box()`-Funktion. Wie der Name schon vermuten lässt, kann man damit Würfel und
Quader in jeder größe erstellen. Ein Würfel ist ein 3D-Objekt, bei dem alle
seiten gleich lang sind. Bei einem Quader können die Seiten unterschiedlich
lang sein.

![3D Shapes][img_3d_shapes]

You can create a Cube or a Cuboid in ScriptCraft using the `box()` 
function. You must tell the function what material you want the shape to 
be made of. For example, in the game, point the cross hairs at the 
ground, then type the following and hit enter...

    /js box("5")

... This will change the targeted block to wood. What's happened here is 
the `box()` function has created a single new wooden block. The text 
`"5"` is taken by Minecraft to mean Wood. You can see many more 
materials and the number Minecraft uses for them by visiting the 
[Minecraft Data Values][mcdv] site.  

### Common Block Materials

In Minecraft Programming, Materials aren't known by their name,
instead numbers (sometimes 2 numbers) are used to indicate which
material should be used. For example the number 2 is grass, 1 is
cobblestone etc, while 5 is wood (oak). There are different types of
wood so the text "5:1" means Spruce, "5:2" means Birch and "5:3" means
Jungle wood. There are many different materials in the Minecraft world, the most
commonly used materials for building are:

 * "4" - Cobblestone 
 * "5" - Wooden Planks
 * "5:2" - Birch wood Planks (light wood)
 * "98" - Stone bricks
 * "45" - Red bricks
 * "68" - Doors
 * "102" - Glass panes (for windows)
   
For reference, here is a chart of all of the blocks (not items) in the Minecraft
world...

![Minecraft Data Values][img_dv]

### Dimensions

`box()` can do more than just
create single blocks - it can create cubes and cuboids of any
size. Take a look at the following picture which shows how shapes are
measured in 3D space. There are 3 dimensions (or sizes) to consider.

1. Width
2. Height
3. Depth (or length) - not to be confused with how deep underground a 
mine-shaft can go. Think of Depth (or length if you prefer) as how far 
away you want something to extend.

![Width, Height and Depth][img_whd]

### Weitere Formen

 * `box0( Block, Breite, Höhe, Tiefe )` - erstellt eine leere Box, also innen hohl – perfekt für Häuser. Decke und Boden werden dabei genauso entfernt.
 * `cylinder( Block, Radius, Höhe )` - erstellt Zylinder, z.B. sehr gut geeignet für Kamine
 * `cylinder0( Block, Radius, Höhe )` - ergibt einen ausgehöhlten Zylinder ohne Decke und Boden – kann sehr gut für Türme verwendet werden.
 * `prism( Block, Breite, Tiefe )` - erstellt dir eine dreieckige Form, die du z.B. für ein typisches Dach verwenden kannst.
 * `prism0( Block, Breite, Tiefe )` - damit kannst du ein ausgehöhltes Dreieck erstellen.

### The Drone Object

ScriptCraft is a Minecraft Mod that lets you execute Javascript code
in the game. It also lets you write your own Mod in Javacript. One
such mod that comes bundled with ScriptCraft is called the `Drone`
mod. The `Drone` is an (invsible) object you create every time you
execute any of the building or movement functions. When you execute...

    /js box(5,3,2,4)
   
... a new `Drone` object is created and does the work of building on
your behalf. Think of a `Drone` as something like a remote control
plane that can move about freely and build things for you. Moving the
Drone is easy...

### Movement

 * `up( numberOfBlocks )` - moves the Drone Up. For example: `up()`
   will move the Drone 1 block up. You can tell it how many blocks to
   move if you want it to move more than one block.
 * `down( numberOfBlocks )` - moves the Drone Down. 
 * `left( numberOfBlocks )` - moves the Drone Left.
 * `right( numberOfBlocs )` - moves the Drone Right.
 * `fwd( numberOfBlocs )` - moves the Drone Forward (away from the player).
 * `back( numberOfBlocs )` - moves the Drone Back (towards the player)
 * `turn( numberOfTurns )` - Turns the Drone Clock-wise (right). For example:
   `turn()` will make the Drone turn right 90 degrees. `turn(2)` will
   make the Drone turn twice so that it is facing in the opposite
   direction.

#### Chaining - combining bulding and movement.

You can make a Drone move around before and after building by
*daisy-chaining* the building and movement functions together. In the
game, point at the ground then type the following...

    /js up(1).box(5).fwd(3).box(5)
   
A series of 2 boxes is created 3 blocks apart.

![Two Boxes 3 blocks apart][img_2boxes]

### Excercise - Build a simple dwelling

OK. You know enough now about the `Drone` functions to be able to
build a simple dwelling. The dwelling should be a hollow building with
a sloped roof. *Don't worry about doors or windows for now*. The walls
should be made of Cobblestone ("4") and the roof made of wood ("5"). You can use
the following `Drone` functions to create a dwelling 7 blocks wide by
3 blocks high by 6 blocks long with a wooden sloped roof. It's up
to you to figure out how. 

 * `up()` 
 * `box0()`
 * `prism0()`

Your dwelling should end up looking something like this...

![Excercise Dwelling][img_ed]

### Remembering where you started.

Sometimes when you're building something big that requires lots of
manoeuvering by your Drone, you need to leave breadcrumbs as you go so
your `Drone` can return to where it started. Every new Drone has a
`"start"` checkpoint that it can return to by executing
`move("start")` ...

    /js box("5").up(3).left(4).box("1").turn(3).fwd(5).right().box("1").move("start")

... A genius would have trouble figuring out how to get back
to where they started. Fortunately, they don't have to - the
`move("start")` function will take the Drone back to its starting
point. 

 * `chkpt( breadCrumb )` - Leaves a mark at your Drone's current
 location so it can return there later. Think of it as giving a name
 to the place where your Drone is located. `chkpt` is short for
 Check-Point - a place in a game where you usually save your
 progress. 
 
 * `move( breadCrumb )` - Moves your Drone to a location you named
 using `chkpt()` . It brings your Drone back to the place where you
 saved it.
 
Both `chkpt()` and `mark()` are useful for when you want to build
complex things that require your Drone to move about a lot ( for
example, Castles, mansions, palaces, etc).

### Saving your work

You can build cool things using the in-game command-prompt and the
`/js` command but sooner or later you'll probably want to build
something more complex and save your commands so you can run them
again when you quit the game and start it up again.

[Notepad++][np] Is a special text editor (like Notepad which comes
installed on every Windows machine) that is well suited for writing
code. If you don't already have it on your machine, you can [install
Notepad++ here][np]. I recommend using NotePad++ rather than plain old
Notepad because it understands Javascript.

### Your First Minecraft Mod!

So, You've learnt a little bit about Javascript and what the Drone()
object can do, let's use that knowledge to create a Minecraft Mod!

Once you've installed Notepad++, Launch it, create a new file and type the following...

    function greet(){
        echo("Hi " + self.name);
    }

... then save the file in a new directory
`craftbukkit/js-plugins/{your_name}` (replace {your_name} with your
own name) and call the file `greet.js` (be sure to change the file-type
option to '*.* All Files' when saving or NotePad++ will add a '.txt'
extension to the filename. Now switch back to the Minecraft game and
type...

    /reload

... to reload all of the server plugins. Your mod has just been loaded. Try it out by typing this command...

    /js greet()

... it should display ...

    Hi {your-username-here}

... where {your-username-here} will be replaced with your own
minecraft username. Congratulations - You've just written your very
first Minecraft Mod! With ScriptCraft installed, writing Minecraft
Mods is as simple as writing a new javascript function and saving it
in a file in the js-plugins directory. This function will now be
avaible every time you launch minecraft.

#### Parameters
If you want to change the `greet()` function so that it displays a
greeting other than "Hi " you can change the code in the `greet()`
function, or better still, you can use *Parameters*. Parameters are
values you provide to a function so that the function behaves
differently each time it is called. 

![greeting][img_greet]

Change the `greet()` function so that it looks like this...

    function greet( greeting ) {
        echo( greeting + self.name );
    }

... Save your greet.js file and issue the /reload command in
minecraft. Now enter the following command in Minecraft...

    greet("Hello ");

... Now try ...

    greet("Dia Dhuit ");

... you should see the following messages in your chat window...

    Hello {your name}
    Dia Dhuit {your name}

... Parameters let you provide different values to functions each time
they're called. As you'll see later, Parameters are very useful when
changing the behaviour of MineCraft.

### true or false

Try entering each of the following statements and make a note of the
answers given by minecraft...

    /js 1 < 2

    /js 1 > 2

... the answer given by the first statement ( `1 < 2` ) should be
`true` since 1 is less than 2. The `<` symbol - usually found near the
bottom right of your keyboard - means test to see if something is less
than another so `1 < 2` is a way of asking the computer "is 1 less
than 2 ?". This is a silly example of course since we know 1 is less
than 2 but when dealing with variables we might not know in advance
what its value is or whether it's greater than (bigger) or less than
(smaller) another number or value. The result of the 2nd statement (`1 > 2`) 
should be `false` since 1 is not greater than 2. Now try this...

    /js 1 = 2

... The result won't be what you expected. You'll see an Error message
- that's OK. What's happened here is I've tried to test to see if 1 is
equal to 2 but I've made one of the most common mistakes even
experienced programmers make. If you want to test to see if two things
are the same, you use `==` that's two equals signs right next to each
other. Let's try again...

    /js 1 == 2

... this time you should get an answer `false` since 1 obviously isn't
equal to 2. These are the different *operators* used when comparing
things...

 * `<`  Is less than ?
 * `>`  Is greater than ?
 * `==`  Is equal to ?
 * `<=`  Is less than or equal to ? 
 * `>=`  Is greather than or equal to ?
 * `!=` Is not equal to ?

... try comparing some more numbers yourself - say for example,
compare the ages of your friends or siblings to your own age.

#### More fun with `true` or `false`
You can find out if you can Fly in minecraft by typing the following statement...

    /js self.allowFlight 

... the result will be `true` or `false` depending on whether you can
fly or not. You can turn on and off your ability to fly by setting
your `allowFlight` property to `true` or `false`. Try it...

    /js self.allowFlight = true

... Now you can fly! To turn off flight...

    /js self.allowFlight = false

... and you come crashing down to earth. This is just one example of
how `true` and `false` are used throughout ScriptCraft - these are
called `boolean` values - named after [George Boole][boole], a 19th Century
Maths Professor at University College Cork. There are plenty more
examples of boolean values in Minecraft. You can find out if monsters
are allowed in your minecraft world by typing the following
statement...

    /js self.location.world.allowMonsters

... The result of this statement will be either `false` (Phew!) or
`true` (Yikes!) depending on how your server has been
configured. However, typing the following statement doesn't work as
expected...

    /js self.location.world.allowMonsters = true

... This statement won't work as expected - it will give an Error
message. This is because sometimes we can read variables but we can't
change them the same way we read them (this is because of how
Javascript, Java and the CraftBukkit API work together). To turn on or
off the spawning of monsters, type the following...

    /js self.location.world.setSpawnFlags(false, true)

... the `setSpawnFlags()` method takes 2 parameters, the first
parameter says whether or not monsters can spawn, and the 2nd says
whether or not Animals can spawn. (SIDENOTE: You may be wondering how
to change other aspects of the Minecraft game - pretty much all
aspects of the game can be changed. Changes are made using what are
called `API` calls - these are calls to functions and methods in
Minecraft - you can read more about these on the [CraftBukkit API
Reference][cbapi].)

### ...and Again, and Again, and Again,...

One of the things Computers are really good at is
repetition. Computers don't get tired or bored of doing the same thing
over and over again.  Loops are handy, if you want to run the same
code over and over again, each time with a different value.  

#### Counting to 100

At the in-game command prompt (hint: press 't') type the following then hit Enter...

    /js for (var i = 1 ; i <= 100 ; i = i + 1) { echo( i ); }

... The above code will count from 1 to 100. The first thing you'll
notice if you run the above code is how quickly the count
happened. You're probably curious how long it would take to count to
1000. Try it out for yourself. Change the above line of code so that
it counts to 1000 instead of 100. If you're feeling adventurous, see
how long it takes to count to ten thousand, one hundred thousand or even one million.

The `for` statement is useful when you want to repeat something over and over. It has 4 parts...

 1. The initialiser: `var i = 1` - this happens once at the start of the loop.
 2. The test: `i <= 100` - this happens at the start of each run around the loop. If the test fails, then the loop ends.
 3. The increment: `i = i + 1` - this happens at the end of each run
 around the loop. If you didn't have a statement here, the loop might
 never finish. `i = i + 1` is often written as `i++` - it's shorter
 and does basically the same thing.
 4. The body - everything that appears between the `{` and `}` (opening and closing curly braces).


`for` loops becomes very useful when you combine it with Arrays -
remember, an Array is just a list of things, for example - the players
connnected to a server, the worlds of a server and so on.

#### Saying "Hi!" to every player

At the in-game command prompt type the following then hit Enter...

    /js for (var i = 0;i < server.onlinePlayers.length; i++){ server.onlinePlayers[i].sendMessage("Hi!"); }

... Lets look at these statements in more detail. We had to enter the
statements on a single line at the in-game command prompt but the
statements could be written like this...

    var players = server.onlinePlayers;
    for (var i = 0; i < players.length; i++) {
        var player = players[i];
        player.sendMessage("Hi!");
    }

... On the first line, a new variable `players` is created from the
server object's onlinePlayers property. `players` is more concise and
easier to type than the long-winded `server.onlinePlayers`.  On the
second line, the for loop is declared, a counter variable `i` is set
to 0 (zero - arrays in javascript start at 0 not 1) and each time
around the loop is tested to see if it's less than the number of
players online. At the end of each run around the loop the `i`
variable is incremented (increased by 1) so that the next player can
be messaged.  Inside the body of the for loop (everything between the
opening `{` and closing `}` curly braces) the `players[i]` expression
refers to the player in the players array at position[i].  Imagine
there are 4 players online on a minecraft server, the `players` array
might look like this...

 * players[0] = 'CrafterJohn'
 * players[1] = 'MinerPaul'
 * players[2] = 'ExplorerRingo'
 * players[3] = 'TraderGeorge'

... in this case `players.length` will be 4 (since there are 4 online
players), the for-loop will go around 4 times starting from position 0
and going all the way up to position 3, sending a message to each of
the players in the array. It's time for a new scriptcraft
function. Open the `hi.js` file you created earlier (using NotePad++ ,
TextWrangler or your editor of choice) and add the following code at
the bottom of the file...

    function hiAll(){
        var players = server.onlinePlayers;
        for (var i = 0; i < players.length; i++) {
            var player = players[i];
            player.sendMessage("Hi!");
        }
    }

... save the file, at the in-game command prompt type `reload` and
then type `/js hiAll()`. This will send the message `Hi!` to all of
the players connected to your server. You've done this using a `for`
loop and arrays. Arrays and `for` loops are used heavily in all types
of software, in fact there probably isn't any software that doesn't
use `for` loops and Arrays to get things done.

#### While Loops

Another way to repeat things over and over is to use a `while`
loop. The following `while` loop counts to 100...

    var i = 1;
    while (i <= 100){
        echo( i );
        i = i + 1;
    } 

A `while` loop will repeat until its condition is `false` - the
condition in the above example is `i <= 100` so while i is less than
or equal to 100 the code within the `while` block (everything between
the starting `{` and ending `}` curly braces) will run. It's important
that you change the variable being tested in a while loop, otherwise
the while loop will never it - it will run forever. Try running the
following code...

    /js var i = 1; while (i <= 100){ echo( i ); }

The code above will contine printing out the number 1 until the end of
time (or until you unplug your computer). That's because the `i`
variable is never incremented (remember - incrementing just means
adding 1 to it) so i will always be 1 and never changes meaning the
loop goes on forever. Again - this is a mistake even experienced programmers sometimes make.

Just like `for` loops, `while` loops can be also be used to loop
through arrays. The following loop prints out all of the players on
the server...

    var players = server.onlinePlayers;
    var i = 0;
    while ( i < players.length ) {
        echo( players[i] );
        i = i + 1;
    }

... whether you chose to use a `for` loop or a `while` loop is largely
a matter of personal taste, `for` loops are more commonly used with
Arrays but as you see from the example above, `while` loops can also
loop over Arrays.

#### `utils.foreach()` - Yet another way to process Arrays

Both the `for` statement and `while` statement are standard commonly
used javascript statements used for looping. ScriptCraft also comes
with a special function for looping called `utils.foreach()`.
utils.foreach() is a convenience function, you don't have to use it if
you prefer the syntax of javascript's `for` and `while`
loops. utils.foreach() takes two parameters...

 1. An array 
 2. A function which will be called for each item in the array. 

...that's right, you can pass functions as parameters in javascript!
Let's see it in action, the following code will `echo()` (print) the
name of each online player...

    utils.foreach( server.onlinePlayers, echo );

... in the above example, the list of online players is processed one
at a time and each item (player) is passed to the `echo`
function. Note here that I used `echo` not `echo()`. The round braces
() are used to call the function. If I want to pass the function as a
parameter, I just use the function name without the round braces. The
above example uses a named function which already exists ( `echo` ),
you can also create new functions on-the-fly and pass them to the
utils.foreach() function...

    /*
      give every player the ability to fly.
    */
    utils.foreach( server.onlinePlayers, 
                   function (player) { 
                       player.setAllowFlight(true); 
                   }
    );

... Another example, this time each player will hear a Cat's Meow...

    /*
      Play a Cat's Meow sound for each player.
    */
    utils.foreach( server.onlinePlayers, 
                   function (player) { 
                       player.playSound(player.location, 
                                        org.bukkit.Sound.CAT_MEOW,
                                        1,
                                        1);

                   }
    );

#### Exercise
Try changing the above function so that different sounds are played
instead of a Cat's Meow.  You'll need to lookup the [CraftBukkit API's
Sound class][soundapi] to see all of the possible sounds that can be
played.

Loops are a key part of programming in any language. Javascript
provides `for` and `while` statements for looping and many javascript
libraries also provide their own custom looping functions. You should
use what you feel most comfortable with.

#### Putting `for` loops to use - Building a Skyscraper

For loops can be used to build enormous structures. In this next
exercise I'm going to use a for loop to build a skyscraper.  This
skyscraper will be made of Glass and Steel (just like most skyscrapers
in real-life).  The first thing to do is see what a single floor of
the skyscraper will look like. Place a block (of any type) where you
want to eventually build the skyscraper, then while your cursor is
pointing at the block, type the following into the in-game prompt...

    /js var drone = box(blocks.iron,20,1,20).up().box0(blocks.glass_pane,20,3,20).up(3)

... you should a large (20x20) iron floor with 3 block high glass all around.

![skyscraper-floor.png][img_ssf]

... A skyscraper with just a single floor isn't much of a skyscraper
so the next step is to repeat this over and over. This is where `for`
loops come in. Open your favorite text editor and create a new file in
your js-plugins/{your-name} directory called `myskyscraper.js`, then
type the following...

    function skyscraper(floors)
    {
        floors = floors || 10; // default number of floors is 10
        this.chkpt('skyscraper'); // saves the drone position so it can return there later
        for (var i = 0; i < floors; i++)
        {
            this.box(blocks.iron,20,1,20).up().box0(blocks.glass_pane,20,3,20).up(3);
        }
        return this.move('skyscraper'); // return to where we started
    };

    load("../drone/drone.js");
    Drone.extend('skyscraper',skyscraper);

... so this takes a little explaining. First I create a new function
called skyscraper that will take a single parameter `floors` so that
when you eventually call the `skyscraper()` function you can tell it
how many floors you want built. The first statement in the function
`floors = floors || 10;` just sets floors to 10 if no parameter is
supplied. The next statement `this.chkpt('myskyscraper')` just saves
the position of the Drone so it can eventually return to where it
started when finished building (I don't want the drone stranded atop
the skyscraper when it's finished). Then comes the `for` loop. I loop
from 0 to `floors` and each time through the loop I build a single
floor. When the loop is done I return the drone to where it started.
The last 2 lines load the drone module (it must be loaded before I can
add new features to it) and the last line extends the 'Drone' object
so that now it can build skyscrapers among other things.  Once you've
typed in the above code and saved the file, type `reload` in your
in-game prompt, then type ...

     /js skyscraper(2);

... A two-story skyscraper should appear. If you're feeling
adventurous, try a 10 story skyscraper! Or a 20 story skyscraper!
Minecraft has a height limit (256 blocks from bedrock) beyond which
you can't build. If you try to build higher than this then building
will stop at that height.

![skyscraper][img_ss]

I'll leave it as an exercise to the reader to create a city block of
skyscrapers, 5 blocks apart using a for loop.  Once you've figured
that out, creating an entire city of blocks of skyscrapers is the next
logical step. Of course, Minecraft doesn't have the same constraints
as real-world densely populated areas so let your imagination go wild.


### Making Decisions 

All the programs we have seen so far have been fairly predictable - they went 
straight through the statements, and then went back to the beginning again. This is 
not very useful. In practice the computer would be expected to make decisions and 
act accordingly. The javascript statement used for making decisions is `if`. 
While standing on the ground in-game, type the following at the command prompt...

    /js if ( self.flying ) { echo("Hey, You are flying!"); }

... No message should appear on screen. That is - `Hey, You are
flying!` should *not* appear on screen.  Now double-tap the `space`
bar to start flying in-game (tap the space bar twice in rapid
succession), then press and hold space to rise above the ground. Now
enter the same statement again (If you don't want to type the same
statement again, just press `/` then press the `UP` cursor key on your
keyboard, the statement you entered previously should reappear.

    /js if ( self.flying ) { echo("Hey, You are flying!"); }

... this time the following message should have appeared on your screen...

    Hey, You are flying!

The `if` statement tests to see if something is `true` or `false` and
if `true` then the block of code between the curly braces ( `{` and
`}` ) is executed - but only if the condition is true.  The condition
in the above example is `self.flying` which will be `true` if you are
currently flying or `false` if you aren't.

What if you wanted to display a message only if a condition is *not*
true ? For example to only display a message if the player is *not*
flying...

    /js if ( ! self.flying ) { echo ("You are not flying."); }

... This code differs in that now there's a `!` (the exclamation mark)
before `self.flying`. The `!` symbol negates (returns the opposite of)
whatever follows it.

What if you want to display a message in both cases - whether you're
flying or not? This is where the `if - else` construct comes in handy.
Open your favorite editor and type the following code into a new file
in your js-plugins directory...

     function flightStatus()
     {
         if ( self.flying ) 
         { 
             echo( "Hey, You are flying!" );
         } 
         else 
         {
             echo( "You are not flying." );
         }
     }

... now type `/reload` at the in-game prompt then type `/js
flightStatus()` and an appropriate message will appear based on
whether or not you're currently flying. Type the `/js flightStatus()`
command while on the ground and while flying. The message displayed in
each case should be different.

### Next Steps

This guide is meant as a gentle introduction to programming and
modding Minecraft using the Javascript Programming Language.
Javascript is a very powerful and widely-used programming language and
there are many more aspects and features of the language which are not
covered here. If you want to dive deeper into programming and modding
minecraft, I recommend reading the accompanying [ScriptCraft API
reference][api] which covers all of the ScriptCraft functions, objects
and methods. I also recommend reading the source code to some of the
existing scriptcraft add-ons, the *chat* module (
`js-plugins/chat/chat.js` ) is a good place to start, followed by
[Anatomy of a ScriptCraft Plug-in][ap].  The online [Craftbukkit API
Reference][cbapi] provides lots of valuable information about the
different objects and methods available for use by ScriptCraft.


[buk]: http://wiki.bukkit.org/Setting_up_a_server
[dlbuk]: http://dl.bukkit.org/
[sc-plugin]: files/scriptcraft/
[ce]: http://www.codecademy.com/
[mcdv]: http://www.minecraftwiki.net/wiki/Data_values
[np]: http://notepad-plus-plus.org/
[cbapi]: http://jd.bukkit.org/beta/apidocs/
[boole]: http://en.wikipedia.org/wiki/George_Boole
[soundapi]: http://jd.bukkit.org/beta/apidocs/org/bukkit/Sound.html
[ap]: http://walterhiggins.net/blog/ScriptCraft-1-Month-later
[api]: api.md

[img_echo_date]: img/ypgpm_echo_date.png
[img_3d_shapes]: img/ypgpm_3dshapes.jpg
[img_whd]: img/ypgpm_whd.jpg
[img_dv]: img/ypgpm_datavalues.png
[img_ed]: img/ypgpm_ex_dwell.png
[img_2boxes]: img/ypgpm_2boxes.png
[img_cr]: img/ypgpm_mc_cr.png
[img_greet]: img/ypgpm_greet.png
[img_ssf]: img/skyscraper_floor.png
[img_ss]: img/skyscraper.png

## Categories
Minecraft, Programming, ScriptCraft