Logo Lesson 1
TBE 540-40
Fall 2004
Farah Fisher
What is Logo?

A programming language (instructions to the
computer to perform a task)
 Created at MIT during a study of artificial
intelligence (see http://el.media.mit.edu/logofoundation/logo/index.html)
 Can be used by virtually any student - from young
children through engineering students
 Can be used to create pictures, display text, or
perform calculations. Some versions can even
make music!
What is Logo?


When Logo is used to create pictures,
commands are given to a “robot turtle”.
Some samples of the “turtle” shape:
What does Logo look like?


The simplest form of Logo uses movement
commands to control the “robot turtle”.
Sample commands:




FD (or FORWARD) moves the turtle forward
BK (or BACK) moves the turtle backwards
RT (or RIGHT) turns the turtle to the right
LT (or LEFT) turns the turtle to the left
What does Logo look like?

Each movement command (FD, BK, RT, LT)
needs more information.
 FD and BK both require a number, which indicates
the “turtle steps” to move (steps are very small).
 RT and LT both require the number of degrees in
the turn.
 Examples (notice the space after the command):
 FD 50 (move forward 50 turtle steps)
 LT 90 (turn left 90 degrees)
What does Logo look like?




As the turtle moves, it leaves a “trail” on the
screen.
These “trails” make shapes.
Imagine for a moment that you are walking
around the bases of a baseball diamond,
about 30 steps on each side. Assume that
you are walking forward from base to base.
Are you turning left or right?
Go to the next slide when you finish.
What does Logo look like?

In walking around the baseball diamond in your
imagination, you probably followed these steps
(written as they would be in Logo):








FD 30 (home to 1st base)
LT 90 (turn toward 2nd base)
FD 30 (1st base to 2nd base)
LT 90 (turn toward 3rd base)
FD 30 (2nd base to 3rd base)
LT 90 (turn toward home)
FD 30 (3rd base to home)
Imagine that you were dragging a paint brush
when you walked. What shape would you have
drawn?
What does Logo look like?

The commands below would make a
square! (turtle shown at the end)
FD 30
LT 90
FD 30
LT 90
FD 30
LT 90
FD 30
What shapes would these make?
SHAPE 1
FD 30
RT 90
FD 60
SHAPE 2
RT 90
FD 50
LT 90
FD 50
SHAPE 3
FD 50
LT 60
FD 50
SHAPE 4
FD 100
RT 45
FD 50
Try these with pencil and paper. Click to check
your answers.
What shapes would these make?
SHAPE 1
FD 30
RT 90
FD 60
SHAPE 2
RT 90
FD 50
LT 90
FD 50
SHAPE 3
FD 50
LT 60
FD 50
SHAPE 4
FD 100
RT 45
FD 50
The REPEAT Command
When you “walked around the bases”, you may
have noticed that the Logo commands were
repeated.
 The REPEAT command is used as a shortcut in
place of writing out repeated commands.
 Example: REPEAT 2 [FD 50 RT 90] is the
equivalent of FD 50 RT 90 FD 50 RT 90
 Notice that the number of repeats comes first, with
the commands to be repeated inside square
brackets.

REPEAT Example

To make a
SQUARE
FD 30
LT 90
FD 30
LT 90
FD 30
LT 90
FD 30

OR…to make a SQUARE
REPEAT 4 [FD 30 LT 90]
This version actually adds
another LT 90 to the list, but
does not change the basic
shape.
More about REPEAT

You have seen that REPEAT 4 [FD 30 LT 90]
makes a square. Guess the shapes made by
the REPEAT commands below. Click to see if
you were right.
REPEAT 3 [FD 30 LT 120]
REPEAT 6 [FD 30 LT 60]
REPEAT 8 [FD 30 LT 45]
REPEAT 5 [FD 30 LT 72]
More about REPEAT
REPEAT 3 [FD 30 RT 120]
REPEAT 6 [FD 30 LT 60]
REPEAT 8 [FD 30 LT 45]
REPEAT 5 [FD 30 LT 72]
Did you notice a pattern?

The number after REPEAT is the number of sides.
 Examine the number of repeats and the number of
degrees. Try multiplying them together. Example:
4 (sides) x 90 (turn)
 The sides x degrees should always be the same
number in the samples you tried.
 Could you use this information to make a 10-sided
figure? Click for a possible answer.
Did you notice a pattern?


REPEAT 10 [FD 30 LT 36] should make a 10-sided figure.
Why? Look at the “total turtle turns” below:
REPEAT 3 [FD 30 LT 120]
REPEAT 6 [FD 30 LT 60]
REPEAT 8 [FD 30 LT 45]
REPEAT 5 [FD 30 LT 72]
REPEAT 10 [FD 30 LT 36]
}
3 x 120 = 360
6 x 60 = 360
8 x 45 = 360
5 x 72 = 360
10 x 36 = 360
When the turtle makes a closed figure (no breaks in the
sides), the total turns add up to 360 degrees.
Logo and Critical Thinking



You have just seen an example of the use of
Logo to enhance critical thinking.
Your students (and you, too) can be
challenged to write the sequential steps
needed to make shapes, look for patterns,
predict outcomes…all part of critical
thinking.
Watch for more examples of critical thinking
as you learn Logo.
Changing Things





Here is another prediction task for you.
You have seen that to make a square, you
can use REPEAT 4 [FD 30 LT 90]
Do you think the same commands would
work if you turned RT instead of LT?
How could you make a square larger? What
would you have to change?
After you have made predictions, go to the
next slide.
Were you correct?
REPEAT 4 [FD 30 LT 90]
REPEAT 4 [FD 10 LT 90]
REPEAT 4 [FD 50 LT 90]
REPEAT 4 [FD 30 RT 90]
Controlling the Logo “Pen”




When the Logo turtle moves, it usually
draws with a “pen”.
This pen can be “down” (draws a line) or
“up” (does not draw a line). If the pen is up,
the turtle moves without drawing.
The pen can also become an eraser
(remove a line already drawn).
The pen color abd background can be
changed.
Pen Control Commands




PU (PENUP) - subsequent movements of
the turtle will not leave a line
PD (PENDOWN) - subsequent movements
of the turtle will leave a line
PE (PENERASE) - subsequent movements
of the turtle will erase any line it crosses
PPT or PP (PENPAINT) - used by some
versions of Logo to “undo” PENERASE
Logo Challenge



How could you use PU and PD to make a
dashed line (like the middle of a road)?
Think about this problem for awhile, then
click for a possible answer.
Try making the pattern below (turtle always
starts pointed “up” with the pen down):
Logo Challenge
Two possible solutions for this shape:
RT 90 FD 25 PU FD 25 PD FD 25 PU FD 25 PD
FD 25 PU FD 25 PD FD 25
(NOTE: Logo commands can be placed on the same line.)
Alternate using REPEAT:
RT 90 REPEAT 4 [FD 25 PU FD 25 PD]
OR…You could draw a line and go back over it with an
eraser!
Logo Color





The Logo command to set the pen color is SETPC
on most versions of Logo.
The Logo commands to set the background color
is SETBG on most versions of Logo.
Each of these commands must be followed by a
number (typically from 0 to 15).
The numbers may signify different colors in
various version of Logo. You will need to
experiment.
NOTE: Some versions of Logo use a menu to
choose colors.
Logo Color





Here are some sample commands using
color.
SETPC 0 (pen will draw in black)
SETPC 7 (pen will draw in white - probably)
SETBG 3 (screen background will change
color)
NOTE: If you set the pen color and the
background to the same number, you will
not see any drawing!
Self-Check for Lesson 1


Suppose you enter these commands (with
the turtle starting at “home” in the middle of
the screen, pointing up): FD 30 RT 90
Which shape would appear?
Self-Check for Lesson 1


Suppose you enter these commands (with
the turtle starting at “home” in the middle of
the screen, pointing up): FD 30 RT 90
Which shape would appear?
Self-Check for Lesson 1

Which of the following is a Logo shortcut for
FD 50 LT 60 FD 50 LT 60 FD 50 LT 60

REPEAT 3 (FD 50 LT 60)
REPEAT [LT 60 FD 50]
REPEAT 3 [FD 50 LT 60]
REPEAT [FD 50 LT 60]



Self-Check for Lesson 1

Which of the following is a Logo shortcut for
FD 50 LT 60 FD 50 LT 60 FD 50 LT 60

REPEAT 3 (FD 50 LT 60)
REPEAT [LT 60 FD 50]
REPEAT 3 [FD 50 LT 60]
REPEAT [FD 50 LT 60]



Self-Check for Lesson 1

Which of the following sets of Logo
commands will move the turtle 50 steps
without drawing?

FD 50 PU
PU FD 50
PE FD 50


Self-Check for Lesson 1

Which of the following sets of Logo
commands will move the turtle 50 steps
without drawing?

FD 50 PU
PU FD 50
PE FD 50


{PENUP starts no drawing} OR
{PENERASE also starts no drawing}
Self-Check for Lesson 1

Suppose you type these three Logo
commands:
 SETBG 0 SETPC 0 FD 100

What will you see on the screen?
Self-Check for Lesson 1

Suppose you type these three Logo
commands:
 SETBG 0 SETPC 0 FD 100

What will you see on the screen?
You will see the turtle in a different place, but
no line. You have instructed the turtle to
draw in black on a black background!
Time to Try Logo


Use the class CD-ROM to start Logo or
download it from the website at
http://www.csudh.edu/fisher/tbe540
You should see two windows - one for
commands and one to show the drawing.
FD 50
RT 90
FD 25
Time to Try Logo


Try the activities from Hands-On Exercise 1.
This is not a graded exercise.
Experiment with the Logo commands listed
on the handout for Week 1.