Example that will be studied to help with Problem #1 on the Homework: The EVEN and the ODD turtles.
1. ca - clear all is abbreviated ca for clear all
- -
Any turtles created with cro or crt are destroyed and removed from
the turtle GRID world.
Any drawings that have been created are erased. Drawing would have been
created with turtles moving about with their PD Pens Down, or pd tails dragging.
360
2. cro - cro 8 create ordered turtles and since ---------- = 45 degrees,
8
the heading or directions of the 8 turtles would be:
0 and 45 and
90 and 135 and
180 and 225 and
270 and 315
cr 36 create ordered turtles with each turtle facing 10 degrees more than
the first turtle.
Headings would be 0, 10, 20, 30, ... , 340, 350
degrees for the 36 turtles.
3. crt n crt 10 creates 10 turtles, but they have random headings.
crt 8 creates 8 turtles, located at (0,0) the same as cro would do,
but they have totally random headings.
You discover the random headings or directions the turtles are
facing when you do the command fd n, such as:
ca
crt 16
ask turtles [ fd 8 ]
would show you that the turtles were facing every which way,
and NOT facing a very symmetric 0, 22.5, 45, 67.5, 90, ... etc.
---
Do you understand the difference between CRO and CRT now?
4. turtles - two vip facts about any turtle at any moment: position and heading
-------- -------
turtles have a position (or location)... 2D = 2 dimensional space = 2D space
The default position of any turtle
created with cro or crt command is (0, 0),
which is the very center of the GRID of
patches, the very center of the turtles 2D
world.
turtles have a heading, or a direction that they are facing and will move in
when asked to go forward with the fd command.
5. pu = pen up - pu or pen up or turtle tail up is the DEFAULT. Any turtle created
by cro or crt will be DEFAULT have its pen up.
pd = pen down - turtle will leave a trail or draw a line when it moves when its
pen is down.
6. fd n - tells the turtle to move forward n steps or a length of n grid units.
- -
fd 5 moves the turtle forward 5 steps.
fd 14 moves the turtle forward 14 steps or grid units.
If a turtle was facing due NORTH on the grid and at center square,
i.e. its position was (0,0), and we told it to move forward 5 units,
with fd 5 command, where would it be?
(0, 5) would be the location of the turtle.
If a turtle was facing to the left, i.e. to due west on the grid,
and at (0, 0) or the default start location for all turtles,
and we said:
fd 14
the turtles
location would now be (-14, 0)
bk n examples bk 3 tell to turtle to move or walk backwards or back
bk 14 - - - -
bk 5 3 or 14 or 5 or 12 steps.
bk 12
7. rt n turn right n degrees rt = RighT examples rt 45 rt 90 rt 10
lt n turn left n degrees lt = LefT examples lt 120 lt 180 lt 14 lt 5
Note: The following two commands would result in exactly the same heading
for any turtle, i.e. are two ways of a turtle obeying an about face command:
rt 180 and lt 180
It just depends on whether you want the turtles to turn clockwise
or to turn counterclockwise.
In any case, every computer would do this SO FAST, you would not be able to tell
which way the turtle turned!
8. repeat n [ what statements you want repeated n times ]
repeat 4 [ fd 10 rt 90 ] draws a square with side length 10 units,
if the PD pen is down with pd.
You don't see the square that the turtle traced
if the pu pen was up with pu instead of pd.
So don't forget to put the pen down with PD when
you want to DRAW some graphics with the turtles!
9. Solution to the equilateral triangle problem from class #2, Thursday, January 14th.
TO triangle
pd
repeat 3 [ fd 10 rt 120 ]
END