Logo Lesson 1

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Logo Lesson 1

• TBE 540-40
• Fall 2004
• Farah Fisher

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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/logo-fou
  ndation/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!

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What is Logo?

• When Logo is used to create pictures, commands
  are given to a robot turtle.
• Some samples of the turtle shape

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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

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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)

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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.

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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?

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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

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What shapes would these make?

• SHAPE 1
• FD 30
• RT 90
• FD 60
• SHAPE 3
• FD 50
• LT 60
• FD 50

• SHAPE 2
• RT 90
• FD 50
• LT 90
• FD 50
• SHAPE 4
• FD 100
• RT 45
• FD 50

Try these with pencil and paper. Click to check
your answers.
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What shapes would these make?

• SHAPE 1
• FD 30
• RT 90
• FD 60
• SHAPE 3
• FD 50
• LT 60
• FD 50

• SHAPE 2
• RT 90
• FD 50
• LT 90
• FD 50
• SHAPE 4
• FD 100
• RT 45
• FD 50

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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.

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REPEAT Example

• To make a SQUARE
• FD 30
• LT 90
• FD 30
• LT 90
• FD 30
• LT 90
• FD 30

• ORto 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.

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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

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More about REPEAT

• REPEAT 3 FD 30 RT 120
• REPEAT 8 FD 30 LT 45

• REPEAT 6 FD 30 LT 60
• REPEAT 5 FD 30 LT 72

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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.

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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 3 x 120 360
• REPEAT 6 FD 30 LT 60 6 x 60 360
• REPEAT 8 FD 30 LT 45 8 x 45 360
• REPEAT 5 FD 30 LT 72 5 x 72 360
• REPEAT 10 FD 30 LT 36 10 x 36 360
• When the turtle makes a closed figure (no breaks
  in the sides), the total turns add up to 360
  degrees.

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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 outcomesall part of
  critical thinking.
• Watch for more examples of critical thinking as
  you learn Logo.

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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.

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Were you correct?

• REPEAT 4 FD 30 LT 90
• REPEAT 4 FD 30 RT 90

• REPEAT 4 FD 10 LT 90
• REPEAT 4 FD 50 LT 90

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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.

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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

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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)

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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
• Alternate using REPEAT
• RT 90 REPEAT 4 FD 25 PU FD 25 PD
• ORYou could draw a line and go back over it with
  an eraser!

(NOTE Logo commands can be placed on the same
line.)
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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.

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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!

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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?

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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?

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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

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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

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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

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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 PENUP starts no drawing OR
• PE FD 50 PENERASE also starts no drawing

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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?

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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!

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Time to Try Logo

• Use the class CD-ROM to start Logo or download it
  from the website at http//www.csudh.edu/fisher/tb
  e540
• You should see two windows - one for commands and
  one to show the drawing.

FD 50 RT 90 FD 25
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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.