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;. There are several commands to move the turtle over the screen. forward forward X forward moves the turtle forward by the amount of X pixels. When the pen is down the turtle will leave a trail. forward can be abbreviated to fw backward backward X backward moves the turtle backward by the amount of X pixels. When the pen is down the turtle will leave a trail. backward can be abbreviated to bw. turnleft turnleft X turnleft commands the turtle to turn an amount of X degrees to the left. turnleft can be abbreviated to tl. turnright turnright X turnrightthe turtle to turn an amount of X degrees to the right. turnright can be abbreviated to tr. direction direction X direction 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. direction can be abbreviated to dir. centre centre centre moves the turtle to the centre on the canvas. go go X,Y go commands the turtle to go to a certain place on the canvas. This place is X pixels from the left of the canvas, and Y pixels form the top of the canvas. Note that using the go command the turtle will not draw a line. gox gox X gox using this command the turtle will move to X pixels from the left of the canvas whilst staying at the same height. goy goy Y gox using this command the turtle will move to Y pixels from the top of the canvas whilst staying at the same distance from the left border of the canvas. 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. penup penup penup lifts the pen from the canvas. When the pen is up no line will be drawn when the turtle moves. See also pendown. penup can be abbreviated to pu. pendown pendown pendown presses the pen down on the canvas. When the pen is press down on the canvas a line will be drawn when the turtle moves. See also penup.pendown can be abbreviated to pd. penwidth penwidth X penwidth sets the width of the pen (the line width) to an amount of X pixels. penwidth can be abbreviated to pw. pencolour pencolour R,G,B pencolor sets the color of the pen. pencolor takes an RGB combination as input. pencolor can be abbreviated to pc. There are several commands to control the canvas. canvassize canvassize X,Y With the canvassize command you can set the size of the canvas. It takes X and Y as input, where X is the new canvas width in pixels, and Y is the new height of the canvas in pixels. canvassize can be abbreviated to cs. canvascolour canvascolour R,G,B canvascolor set the color of the canvas. canvascolor takes an RGB combination as input. canvascolor can be abbreviated to cc. wrapon wrapon With the wrapon command you can set wrapping on for the canvas. Please see the glossary if you want to know what wrapping is. wrapoff wrapoff With the wrapoff command you can set wrapping off for the canvas: this means the turtle can move off the canvas and can get lost. Please see the glossary if you want to know what wrapping is. There are two commands to clean up the canvas after you have made a mess. clear clear With clear 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. clear can be abbreviated to ccl. reset reset reset cleans much more thoroughly than the clear command. After a reset 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. 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 sprites). So the turtle is a sprite. Next you will find a full overview on all commands to work with sprites. [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] show show show makes the turtle visible again after it has been hidden.show can be abbreviated to ss. hide hide hide hides the turtle. This can be used if the turtle does not fit in your drawing.hide can be abbreviated to sh. The answer is: yes. The turtle can write: it writes just about everything you command it to. print print X The print command is used to command the turtle to write something on the canvas. print takes numbers and strings as input. You can print various numbers and strings using the + symbol. See here a small example: year = 2004 author = "Cies" print "KTurtle was made in " + year + " by " + author fontsize fontsize X fontsize sets the size of the font that is used by print. fontsize takes one input which should be a number. The size is set in pixels. There is one command that rolls a dice for you random random X,Y random 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: repeat 500 [ x = random 1,20 forward x turnleft 10 - x ] Using the random command you can add a bit of chaos to your program. 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 variables, containers that can contain text are called strings. Containers that are not used yet are 0 by default. An example: print N This will print a 0. Let us start with an example: x = 3 print x In the first line the letter x made into a variable (number container). As you see the value of the variable x is set to 3. On the second line the value is printed. Note that if we wanted to print an x that we should have written print "x" That was easy, now a bit harder example: 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 In the first two lines the variables A and B are set to 2004 and 25. On the third line the variable AB is set to A + B, which is 2029. The rest of the example consists of 3 print commands with backward 30 in between. The backward 30 is there to make sure every output is on a new line. In this example you also see that variables can be used in mathematical calculations. Strings are a lot like variables. The biggest difference is that strings cannot be used in mathematical calculations and questions. An example of the use of strings: x = "Hello " name = inputwindow "Please enter your name..." print x + name + ", how are you?" On the first line the string x is set to Hello . On the second line the string name is set to the output of the inputwindow command. On the third line the program prints a composition of three strings on the canvas. This program ask you to enter your name. When you, for instance, enter the name Paul, the program prints Hello Paul, how are you?. Please note that the plus (+) is the only math symbol that you can use with strings. Yes, &kturtle; will do your math. You can add (+), substract (-), multiply (*), and divide (/). Here is an example in which we use all of them: a = 20 - 5 b = 15 * 2 c = 30 / 30 d = 1 + 1 print "a: "+a+", b: "+b+", c: "+c+", d: "+d Do you know what value a, b, c and d have? If you just want a simple calculation to be done you can do something like this: print 2004-12 Now an example with brackets: print ( ( 20 - 5 ) * 2 / 30 ) + 1 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). if and while are execution controllers that we will discuss in the next section. In this section we use the if command to explain questions. A simple example of questions: x = 6 if x > 5 [ print "hello" ] In this example the question is the x > 5 part. If the answer to this question is true the code between the brackets will be executed. Questions are an important part of programming and often used together with execution controllers, like if. All numbers and variables (number containers) can be compared to each other with questions. Here are all possible questions: a == b equals answer is true if a equals b a != b not-equal answer is true if a does not equal b a > b greater than answer is true if a is greater than b a < b smaller than answer is true if a is smaller than b a >= b greater than or equals answer is true if a is greater than or equals b a <= b smaller than or equals answer is true if a is smaller than or equals b Questions can also be glued to each other with question glue, this way a few questions can become one big question. a = 1 b = 5 if a < 5 and b == 5 [ print "hello" ] In this example the glue-word and is used to glue 2 questions (a < 5, b == 5) together. If one side of the and would answer false the whole question would answer false, because with the glue-word and both sides need to be true in order to answer true. and is not the only glue-word there are two others. They are all in the next table: and both sides need to be true in order to answer true or if one of the sides is true the answer is true not only if both of the sides are false the answer is false The execution controllers enable you — as their name implies — to control execution. 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. wait wait X wait makes the turtle wait for X seconds. repeat 36 [ forward 5 turnright 10 wait 0.5 ] 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. if if question [ ... ] The code that is placed between the brackets will only be executed if the answer to the question is true. Please read for more information on questions in the question section. x = 6 if x > 5 [ print "x is greater than five!" ] On the first line x is set to 6. On the second line the question x > 5 is asked. Since the answer to this question is true the execution controller if will allow the code between the brackets to be executed while while question [ ... ] The execution controller while is a lot like if. The difference is that while keeps repeating the code between the brackets till the answer to the question is false. x = 1 while x < 5 [ forward 10 wait 1 x = x + 1 ] On the first line x is set to 1. On the second line the question x < 5 is asked. Since the answer to this question is true the execution controller while starts executing the code between the brackets till the answer to the question is false. In this case the code between the brackets will be executed 4 times, because every time the fifth line is executed x increases by 1.. else if question [ ... ] else [ ... ] else can be used in addition to the execution controller if. The code between the brackets after else is only executed if the answer to the question that is asked is false. x = 4 if x > 5 [ print "x is greater than five!" ] else [ print "x is smaller than six!" ] The question asks if x is greater than 5. Since x is set to 4 on the first line the answer to the question is false. This means the code between the brackets after else gets executed. for for start point to end point [ ... ] The for loop is a counting loop, &ie; it keeps count for you. for x = 1 to 10 [ print x * 7 forward 15 ] Every time the code between the brackets is executed the x is increased by 1, till x reaches the value of 10. The code between the brackets prints the x multiplied by 7. After this program finishes its execution you will see the times table of 7 on the canvas. learn is a very special command, because it is used to create your own commands. The command you create can take input and return output. Let us take a look at how a new command is created: learn circle (x) [ repeat 36 [ forward x turnleft 10 ] ] The new command is called circle. circle takes one input, a number, to set the size of the circle. circle returns no output. The circle command can now be used like a normal command in the rest of the code. See this example: learn circle (x) [ repeat 36 [ forward x turnleft 10 ] ] go 30,30 circle(20) go 40,40 circle(50) In the next example a command with a return value is created. 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) In this example a new command called multiplyBySelf is created. The input of this command is multiplied by it self and then returned, using the return command. The return command is the way to output a value from a function you have created.