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diff --git a/tde-i18n-en_GB/docs/kdeedu/kturtle/programming-reference.docbook b/tde-i18n-en_GB/docs/kdeedu/kturtle/programming-reference.docbook new file mode 100644 index 00000000000..5e459b562f1 --- /dev/null +++ b/tde-i18n-en_GB/docs/kdeedu/kturtle/programming-reference.docbook @@ -0,0 +1,1209 @@ +<chapter id="reference"> +<title +>&kturtle;'s &logo; Programming Reference</title> + +<sect1 id="commands"> +<title +>Commands</title> +<para +>Using commands you tell the turtle or &kturtle; to do something. Some commands need input, some give output. In this section we explain all the commands that can be used in &kturtle;.</para> + +<sect2 id="moving-the-turtle"> +<title +>Moving the turtle</title> +<para +>There are several commands to move the turtle over the screen.</para> + + <variablelist> + <anchor id="forward"/> + <varlistentry> + <term +>forward</term> + <listitem +><para +><screen +>forward X</screen> +<userinput +>forward</userinput +> moves the turtle forward by the amount of X pixels. When the pen is down the turtle will leave a trail. <userinput +>forward</userinput +> can be abbreviated to <userinput +>fw</userinput +></para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="backward"/> + <varlistentry> + <term +>backward</term> + <listitem +><para +><screen +>backward X</screen> +<userinput +>backward</userinput +> moves the turtle backward by the amount of X pixels. When the pen is down the turtle will leave a trail. <userinput +>backward</userinput +> can be abbreviated to <userinput +>bw</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="turnleft"/> + <varlistentry> + <term +>turnleft</term> + <listitem +><para +><screen +>turnleft X</screen> +<userinput +>turnleft</userinput +> commands the turtle to turn an amount of X degrees to the left. <userinput +>turnleft</userinput +> can be abbreviated to <userinput +>tl</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="turnright"/> + <varlistentry> + <term +>turnright</term> + <listitem +><para +><screen +>turnright X</screen> +<userinput +>turnright</userinput +>the turtle to turn an amount of X degrees to the right. <userinput +>turnright</userinput +> can be abbreviated to <userinput +>tr</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="direction"/> + <varlistentry> + <term +>direction</term> + <listitem +><para +><screen +>direction X</screen> +<userinput +>direction</userinput +> set the turtle's direction to an amount of X degrees counting from zero, and thus is not relative to the turtle's previous direction. <userinput +>direction</userinput +> can be abbreviated to <userinput +>dir</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="center"/> + <varlistentry> + <term +>centre</term> + <listitem +><para +><screen +>centre</screen> +<userinput +>centre</userinput +> moves the turtle to the centre on the canvas.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="go"/> + <varlistentry> + <term +>go</term> + <listitem +><para +><screen +>go X,Y</screen> +<userinput +>go</userinput +> commands the turtle to go to a certain place on the canvas. This place is X <glossterm linkend="pixels" +>pixels</glossterm +> from the left of the canvas, and Y <glossterm linkend="pixels" +>pixels</glossterm +> form the top of the canvas. Note that using the <userinput +>go</userinput +> command the turtle will not draw a line.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="gox"/> + <varlistentry> + <term +>gox</term> + <listitem +><para +><screen +>gox X</screen> +<userinput +>gox</userinput +> using this command the turtle will move to X <glossterm linkend="pixels" +>pixels</glossterm +> from the left of the canvas whilst staying at the same height.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="goy"/> + <varlistentry> + <term +>goy</term> + <listitem +><para +><screen +>goy Y</screen> +<userinput +>gox</userinput +> using this command the turtle will move to Y <glossterm linkend="pixels" +>pixels</glossterm +> from the top of the canvas whilst staying at the same distance from the left border of the canvas.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="pen"> +<title +>The turtle has a pen</title> +<para +>The turtle has a pen that draws a line when the turtle moves. There are a few commands to control the pen. In this section we explain these commands.</para> + <variablelist> + <anchor id="penup"/> + <varlistentry> + <term +>penup</term> + <listitem +><para +><screen +>penup</screen> +<userinput +>penup</userinput +> lifts the pen from the canvas. When the pen is <quote +>up</quote +> no line will be drawn when the turtle moves. See also <userinput +>pendown</userinput +>. <userinput +>penup</userinput +> can be abbreviated to <userinput +>pu</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="pendown"/> + <varlistentry> + <term +>pendown</term> + <listitem +><para +><screen +>pendown</screen> +<userinput +>pendown</userinput +> presses the pen down on the canvas. When the pen is press <quote +>down</quote +> on the canvas a line will be drawn when the turtle moves. See also <userinput +>penup</userinput +>.<userinput +>pendown</userinput +> can be abbreviated to <userinput +>pd</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="penwidth"/> + <varlistentry> + <term +>penwidth</term> + <listitem +><para +><screen +>penwidth X</screen> +<userinput +>penwidth</userinput +> sets the width of the pen (the line width) to an amount of X <glossterm linkend="pixels" +>pixels</glossterm +>. <userinput +>penwidth</userinput +> can be abbreviated to <userinput +>pw</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="pencolor"/> + <varlistentry> + <term +>pencolour</term> + <listitem +><para +><screen +>pencolour R,G,B</screen> +<userinput +>pencolor</userinput +> sets the color of the pen. <userinput +>pencolor</userinput +> takes an <glossterm linkend="rgb" +>RGB combination</glossterm +> as input. <userinput +>pencolor</userinput +> can be abbreviated to <userinput +>pc</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="canvas"> +<title +>Commands to control the canvas</title> +<para +>There are several commands to control the canvas.</para> + <variablelist> + <anchor id="canvassize"/> + <varlistentry> + <term +>canvassize</term> + <listitem +><para +><screen +>canvassize X,Y</screen> +With the <userinput +>canvassize</userinput +> command you can set the size of the canvas. It takes X and Y as input, where X is the new canvas width in <glossterm linkend="pixels" +>pixels</glossterm +>, and Y is the new height of the canvas in <glossterm linkend="pixels" +>pixels</glossterm +>. <userinput +>canvassize</userinput +> can be abbreviated to <userinput +>cs</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="canvascolor"/> + <varlistentry> + <term +>canvascolour</term> + <listitem +><para +><screen +>canvascolour R,G,B</screen> +<userinput +>canvascolor</userinput +> set the color of the canvas. <userinput +>canvascolor</userinput +> takes an <glossterm linkend="rgb" +>RGB combination</glossterm +> as input. <userinput +>canvascolor</userinput +> can be abbreviated to <userinput +>cc</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="wrapon"/> + <varlistentry> + <term +>wrapon</term> + <listitem +><para +><screen +>wrapon</screen> +With the <userinput +>wrapon</userinput +> command you can set <glossterm linkend="wrapping" +>wrapping</glossterm +> <quote +>on</quote +> for the canvas. Please see the glossary if you want to know what <glossterm linkend="wrapping" +>wrapping</glossterm +> is.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="wrapoff"/> + <varlistentry> + <term +>wrapoff</term> + <listitem +><para +><screen +>wrapoff</screen> +With the <userinput +>wrapoff</userinput +> command you can set <glossterm linkend="wrapping" +>wrapping</glossterm +> <quote +>off</quote +> for the canvas: this means the turtle can move off the canvas and can get <quote +>lost</quote +>. Please see the glossary if you want to know what <glossterm linkend="wrapping" +>wrapping</glossterm +> is.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="clean"> +<title +>Commands to clean up</title> +<para +>There are two commands to clean up the canvas after you have made a mess.</para> + <variablelist> + <anchor id="clear"/> + <varlistentry> + <term +>clear</term> + <listitem +><para +><screen +>clear</screen> +With <userinput +>clear</userinput +> you can clean all drawings from the canvas. All other things remain: the position and angle of the turtle, the canvascolor, the visibility of the turtle, and the canvas size. <userinput +>clear</userinput +> can be abbreviated to <userinput +>ccl</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="reset"/> + <varlistentry> + <term +>reset</term> + <listitem +><para +><screen +>reset</screen> +<userinput +>reset</userinput +> cleans much more thoroughly than the <userinput +>clear</userinput +> command. After a <userinput +>reset</userinput +> command everything is like is was when you had just started &kturtle;. The turtle is positioned at the middle of the screen, the canvas color is white, and the turtle draws a black line on the canvas.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="sprites"> +<title +>The turtle is a sprite</title> +<para +>Many people do not know what sprites are, so here a short explanation: sprites are small pictures that can be moved around the screen. (for more info see the glossary on <glossterm linkend="sprites" +>sprites</glossterm +>). So the turtle is a sprite.</para> +<para +>Next you will find a full overview on all commands to work with sprites.</para> +<para +>[The current version of &kturtle; does not yet support the use of sprites other than the turtle. With future versions you will be able to change the turtle into something of your own design]</para> + <variablelist> + <anchor id="show"/> + <varlistentry> + <term +>show</term> + <listitem +><para +><screen +>show</screen> +<userinput +>show</userinput +> makes the turtle visible again after it has been hidden.<userinput +>show</userinput +> can be abbreviated to <userinput +>ss</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="hide"/> + <varlistentry> + <term +>hide</term> + <listitem +><para +><screen +>hide</screen> +<userinput +>hide</userinput +> hides the turtle. This can be used if the turtle does not fit in your drawing.<userinput +>hide</userinput +> can be abbreviated to <userinput +>sh</userinput +>.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="writing"> +<title +>Can the turtles write text?</title> +<para +>The answer is: <quote +>yes</quote +>. The turtle can write: it writes just about everything you command it to.</para> + <variablelist> + <anchor id="print"/> + <varlistentry> + <term +>print</term> + <listitem +><para +><screen +>print X</screen> +The <userinput +>print</userinput +> command is used to command the turtle to write something on the canvas. <userinput +>print</userinput +> takes numbers and strings as input. You can <userinput +>print</userinput +> various numbers and strings using the <quote +>+</quote +> symbol. See here a small example: <screen +>year = 2004 +author = "Cies" +print "KTurtle was made in " + year + " by " + author +</screen> + </para +></listitem> + </varlistentry> + </variablelist> + <variablelist> + <anchor id="fontsize"/> + <varlistentry> + <term +>fontsize</term> + <listitem +><para +><screen +>fontsize X</screen> +<userinput +>fontsize</userinput +> sets the size of the font that is used by <userinput +>print</userinput +>. <userinput +>fontsize</userinput +> takes one input which should be a number. The size is set in <glossterm linkend="pixels" +>pixels</glossterm +>.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="dice"> +<title +>A command that rolls a dice for you</title> +<para +>There is one command that rolls a dice for you</para> + <variablelist> + <anchor id="random"/> + <varlistentry> + <term +>random</term> + <listitem +><para +><screen +>random X,Y</screen> +<userinput +>random</userinput +> is a command that takes input and gives output. As input are required two numbers, the first (X) sets the minimum output, the second (Y) sets the maximum. The output is a randomly chosen number that is equal or greater then the minimum and equal or smaller than the maximum. Here a small example: <screen> +repeat 500 [ + x = random 1,20 + forward x + turnleft 10 - x +] +</screen +> Using the <userinput +>random</userinput +> command you can add a bit of chaos to your program.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> +</sect1> + +<sect1 id="containers"> +<title +>Containers</title> +<para +>Containers are letters or words that can be used by the programmer to store a number or a text. Containers that contain a number are called <link linkend="variables" +>variables</link +>, containers that can contain text are called <link linkend="strings" +>strings</link +>.</para> + +<para +>Containers that are not used yet are 0 by default. An example: <screen> +print N +</screen +> This will print a 0. </para> + +<sect2 id="variables"> +<title +>Variables: number containers</title> +<para +>Let us start with an example: <screen> +x = 3 +print x +</screen +> In the first line the letter <userinput +>x</userinput +> made into a variable (number container). As you see the value of the variable <userinput +>x</userinput +> is set to 3. On the second line the value is printed.</para> +<para +>Note that if we wanted to print an <quote +>x</quote +> that we should have written <screen +>print "x" +</screen> +</para> +<para +>That was easy, now a bit harder example: <screen> +A = 2004 +B = 25 +AB = A + B + +# the next command prints "2029" +print AB +backward 30 +# the next command prints "2004 plus 25" +print "" + A + " plus " + B +backward 30 +# the next command prints "1979" +print A - B +</screen +> In the first two lines the variables <userinput +>A</userinput +> and <userinput +>B</userinput +> are set to 2004 and 25. On the third line the variable <userinput +>AB</userinput +> is set to <userinput +>A + B</userinput +>, which is 2029. The rest of the example consists of 3 <userinput +>print</userinput +> commands with <userinput +>backward 30</userinput +> in between. The <userinput +>backward 30</userinput +> is there to make sure every output is on a new line. In this example you also see that variables can be used in <link linkend="math" +>mathematical calculations</link +>.</para> +</sect2> + +<sect2 id="strings"> +<title +>Strings: text containers</title> +<para +>Strings are a lot like variables. The biggest difference is that strings cannot be used in <link linkend="math" +>mathematical calculations</link +> and <link linkend="questions" +>questions</link +>. An example of the use of strings: <screen> +x = "Hello " +name = inputwindow "Please enter your name..." +print x + name + ", how are you?" +</screen +> On the first line the string <userinput +>x</userinput +> is set to <quote +>Hello </quote +>. On the second line the string <userinput +>name</userinput +> is set to the output of the <userinput +>inputwindow</userinput +> command. On the third line the program prints a composition of three strings on the canvas.</para> +<para +>This program ask you to enter your name. When you, for instance, enter the name <quote +>Paul</quote +>, the program prints <quote +>Hello Paul, how are you?</quote +>. Please note that the plus (+) is the only math symbol that you can use with strings.</para> +</sect2> +</sect1> + +<sect1 id="math"> +<title +>Can the Turtle do maths?</title> +<para +>Yes, &kturtle; will do your math. You can add (+), substract (-), multiply (*), and divide (/). Here is an example in which we use all of them: <screen> +a = 20 - 5 +b = 15 * 2 +c = 30 / 30 +d = 1 + 1 +print "a: "+a+", b: "+b+", c: "+c+", d: "+d +</screen +> Do you know what value a, b, c and d have?</para> +<para +>If you just want a simple calculation to be done you can do something like this: <screen +>print 2004-12 +</screen +></para> +<para +>Now an example with brackets: <screen> +print ( ( 20 - 5 ) * 2 / 30 ) + 1 +</screen +> The expressions inside brackets will be calculated first. In this example, 20-5 will be calculated, then multiplied by 2, divided by 30, and then 1 is added (giving 2).</para> +</sect1> + +<sect1 id="questions"> +<title +>Asking questions, getting answers...</title> +<para +><link linkend="if" +><userinput +>if</userinput +></link +> and <link linkend="while" +><userinput +>while</userinput +></link +> are <link linkend="controlling-execution" +>execution controllers</link +> that we will discuss in the next section. In this section we use the <userinput +>if</userinput +> command to explain questions.</para> +<para +>A simple example of questions: <screen> +x = 6 +if x > 5 [ + print "hello" +] +</screen +> In this example the question is the <userinput +>x > 5</userinput +> part. If the answer to this question is <quote +>true</quote +> the code between the brackets will be executed. Questions are an important part of programming and often used together with <link linkend="controlling-execution" +>execution controllers</link +>, like <link linkend="if" +><userinput +>if</userinput +></link +>. All numbers and <link linkend="variables" +>variables</link +> (number containers) can be compared to each other with questions.</para> +<para +>Here are all possible questions: <table> +<title +>Types of questions</title> +<tgroup cols="3"> +<tbody> +<row> +<entry +><userinput +>a == b</userinput +></entry> +<entry +>equals</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> equals <userinput +>b</userinput +></entry> +</row> +<row> +<entry +><userinput +>a != b</userinput +></entry> +<entry +>not-equal</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> does not equal <userinput +>b</userinput +></entry> +</row> +<row> +<entry +><userinput +>a > b</userinput +></entry> +<entry +>greater than</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> is greater than <userinput +>b</userinput +></entry> +</row> +<row> +<entry +><userinput +>a < b</userinput +></entry> +<entry +>smaller than</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> is smaller than <userinput +>b</userinput +></entry> +</row> +<row> +<entry +><userinput +>a >= b</userinput +></entry> +<entry +>greater than or equals</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> is greater than or equals <userinput +>b</userinput +></entry> +</row> +<row> +<entry +><userinput +>a <= b</userinput +></entry> +<entry +>smaller than or equals</entry> +<entry +>answer is <quote +>true</quote +> if <userinput +>a</userinput +> is smaller than or equals <userinput +>b</userinput +></entry> +</row> +</tbody> +</tgroup> +</table> +</para> +<para +>Questions can also be glued to each other with <quote +>question glue</quote +>, this way a few questions can become one big question. <screen> +a = 1 +b = 5 +if a < 5 and b == 5 [ + print "hello" +] +</screen +> <anchor id="question-glue"/>In this example the glue-word <userinput +>and</userinput +> is used to glue 2 questions (<userinput +>a < 5</userinput +>, <userinput +>b == 5</userinput +>) together. If one side of the <userinput +>and</userinput +> would answer <quote +>false</quote +> the whole question would answer <quote +>false</quote +>, because with the glue-word <userinput +>and</userinput +> both sides need to be <quote +>true</quote +> in order to answer <quote +>true</quote +>.</para> +<para +><userinput +>and</userinput +> is not the only glue-word there are two others. They are all in the next table: <table> +<title +>Question glue-words</title> +<tgroup cols="2"> +<tbody> +<row> +<entry +><userinput +>and</userinput +></entry> +<entry +>both sides need to be <quote +>true</quote +> in order to answer <quote +>true</quote +></entry> +</row> +<row> +<entry +><userinput +>or</userinput +></entry> +<entry +>if one of the sides is <quote +>true</quote +> the answer is <quote +>true</quote +></entry> +</row> +<row> +<entry +><userinput +>not</userinput +></entry> +<entry +>only if both of the sides are <quote +>false</quote +> the answer is <quote +>false</quote +></entry> +</row> +</tbody> +</tgroup> +</table> +</para> +</sect1> + +<sect1 id="controlling-execution"> +<title +>Controlling execution</title> +<para +>The execution controllers enable you — as their name implies — to control execution.</para> + +<sect2 id="easy"> +<title +>Have the turtle wait</title> +<para +>If you have done some programming in &kturtle; you have might noticed that the turtle can be very quick at drawing. This command makes the turtle wait for a given amount of time.</para> + <variablelist> + <anchor id="wait"/> + <varlistentry> + <term +>wait</term> + <listitem +><para +><screen +>wait X</screen> +<userinput +>wait</userinput +> makes the turtle wait for X seconds. <screen> +repeat 36 [ + forward 5 + turnright 10 + wait 0.5 +] +</screen +> This code draws a circle, but the turtle will wait half a second after each step. This gives the impression of a slow-moving turtle.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="execute-if"> +<title +>Execute "if"</title> +<para +></para> + <variablelist> + <anchor id="if"/> + <varlistentry> + <term +>if</term> + <listitem +><para +><screen +>if <link linkend="questions" +>question</link +> [ ... ]</screen> +The code that is placed between the brackets will only be executed <userinput +>if</userinput +> the answer to the <link linkend="questions" +>question</link +> is <quote +>true</quote +>. Please read for more information on <link linkend="questions" +>questions</link +> in the <link linkend="questions" +>question section</link +>. <screen> +x = 6 +if x > 5 [ + print "x is greater than five!" +] +</screen +> On the first line <userinput +>x</userinput +> is set to 6. On the second line the <link linkend="questions" +>question</link +> <userinput +>x > 5</userinput +> is asked. Since the answer to this question is <quote +>true</quote +> the execution controller <userinput +>if</userinput +> will allow the code between the brackets to be executed</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="execute-while"> +<title +>Execute "while"</title> +<para +></para> + <variablelist> + <anchor id="while"/> + <varlistentry> + <term +>while</term> + <listitem +><para +><screen +>while <link linkend="questions" +>question</link +> [ ... ]</screen> +The execution controller <userinput +>while</userinput +> is a lot like <link linkend="if" +><userinput +>if</userinput +></link +>. The difference is that <userinput +>while</userinput +> keeps repeating the code between the brackets till the answer to the <link linkend="questions" +>question</link +> is <quote +>false</quote +>. <screen> +x = 1 +while x < 5 [ + forward 10 + wait 1 + x = x + 1 +] +</screen +> On the first line <userinput +>x</userinput +> is set to 1. On the second line the <link linkend="questions" +>question</link +> <userinput +>x < 5</userinput +> is asked. Since the answer to this question is <quote +>true</quote +> the execution controller <userinput +>while</userinput +> starts executing the code between the brackets till the answer to the <link linkend="questions" +>question</link +> is <quote +>false</quote +>. In this case the code between the brackets will be executed 4 times, because every time the fifth line is executed <userinput +>x</userinput +> increases by 1..</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="if-else"> +<title +>If not, in other words: "else"</title> +<para +></para> + <variablelist> + <anchor id="else"/> + <varlistentry> + <term +>else</term> + <listitem +><para +><screen +>if question [ ... ] else [ ... ]</screen> +<userinput +>else</userinput +> can be used in addition to the execution controller <link linkend="if" +><userinput +>if</userinput +></link +>. The code between the brackets after <userinput +>else</userinput +> is only executed if the answer to the <link linkend="questions" +>question</link +> that is asked is <quote +>false</quote +>. <screen> +x = 4 +if x > 5 [ + print "x is greater than five!" +] else [ + print "x is smaller than six!" +] +</screen +> The <link linkend="questions" +>question</link +> asks if <userinput +>x</userinput +> is greater than 5. Since <userinput +>x</userinput +> is set to 4 on the first line the answer to the question is <quote +>false</quote +>. This means the code between the brackets after <userinput +>else</userinput +> gets executed.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +<sect2 id="for-loop"> +<title +>The "for" loop</title> +<para +></para> + <variablelist> + <anchor id="for"/> + <varlistentry> + <term +>for</term> + <listitem +><para +><screen +>for <userinput +>start point</userinput +> to <userinput +>end point</userinput +> [ ... ]</screen> +The <userinput +>for</userinput +> loop is a <quote +>counting loop</quote +>, &ie; it keeps count for you. <screen> +for x = 1 to 10 [ + print x * 7 + forward 15 +] +</screen +> Every time the code between the brackets is executed the <userinput +>x</userinput +> is increased by 1, till <userinput +>x</userinput +> reaches the value of 10. The code between the brackets prints the <userinput +>x</userinput +> multiplied by 7. After this program finishes its execution you will see the times table of 7 on the canvas.</para +></listitem> + </varlistentry> + </variablelist> +</sect2> + +</sect1> + + +<sect1 id="learn"> +<title +>Create your own commands</title> +<para +><userinput +>learn</userinput +> is a very special command, because it is used to create your own commands. The command you create can take <glossterm linkend="input-output" +>input</glossterm +> and return <glossterm linkend="input-output" +>output</glossterm +>. Let us take a look at how a new command is created: <screen> +learn circle (x) [ + repeat 36 [ + forward x + turnleft 10 + ] +] +</screen +> The new command is called <userinput +>circle</userinput +>. <userinput +>circle</userinput +> takes one <glossterm linkend="input-output" +>input</glossterm +>, a number, to set the size of the circle. <userinput +>circle</userinput +> returns no <glossterm linkend="input-output" +>output</glossterm +>. The <userinput +>circle</userinput +> command can now be used like a normal command in the rest of the code. See this example: <screen +>learn circle (x) [ + repeat 36 [ + forward x + turnleft 10 + ] + ] + + go 30,30 + circle(20) + + go 40,40 + circle(50) +</screen> +</para> +<para +>In the next example a command with a return value is created. <screen> +reset + +learn multiplyBySelf (n) [ + r = n * 1 + r = n * n + return r +] +i = inputwindow "Please enter a number and press OK" +print i + " multiplied by itself is: " + multiplyBySelf (i) +</screen +> In this example a new command called <userinput +>multiplyBySelf</userinput +> is created. The input of this command is multiplied by it self and then returned, using the <anchor id="return"/><userinput +>return</userinput +> command. The <userinput +>return</userinput +> command is the way to output a value from a function you have created. </para> +</sect1> + +</chapter> |