B.A. (Mahayana Studies)
000-209 Introduction to Computer Science
November 2005 - March 2006
12. Logo (Part 1)
 An
introduction to Logo:
drawing, moving, turning,
repetition, and basic procedures.
Overview






1. What is Logo?
2. Installing Logo
3. Basic Commands
4. Drawing a Square
5. More Commands
6. The Repeat Command
continued
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





7. Procedures
8. Circle and Square
9. Drawing a Triangle
10. Drawing a House
11. Drawing a Checkboard
12. MSW Logo Examples
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1. What is Logo?

A programming language developed at the MIT
Artificial Intelligence Lab
 MIT
= Massachusetts Institute of Technology

Logo is easy to learn, but powerful.

Logo has been used in telecommunications,
multimedia, and robotics.
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2. Installing Logo

We're using MSW Logo,
but there are many other
Logo systems.
MSW Logo Website:
 http://www.softronix.com/logo.html

The set-up kit (Windows installer):
 http://www.softronix.com/download/mswlogo65.exe

Tutorials
 The
Great Logo Adventure
http://www.softronix.com/download/tgla.zip
 An Introduction to MSW Logo
http://www.southwest.com.au/~jfuller/logotut/menu.htm
continued
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
Double click on mswlogo65.exe to start the
installation.

The program will be added to the start menu as
"Microsoft Windows Logo".
 called

MSW Logo
The MSWLogo directory contains an Examples/
folder (see end of these slides).
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MSW Logo in Action
menus
the turtle
status
window
editor
turtle drawing
area
command
window
command
box
command input window
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What is the Turtle?

Originally, the turtle was a robot
that moved around the floor when the user typed
Logo commands into a computer.

Today, it is a picture on the Logo drawing area
 in
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MSW Logo, the turtle is drawn as a triangle
8
3. Basic Commands

forward <number>
 the
larger the number the farther the turtle will go
 if you use a large enough number, the turtle will walk
off the screen and wrap around to the other side
 e.g. forward 40

back <number>
 the
turtle will move backwards
 e.g. back 33
continued
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
right <number>
 the
number is how many degrees the turtle will turn
right
 e.g. RIGHT 90


turn the turtle to the right by 90 degrees.
left <number>
 turns
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the turtle to the left
10
4. Drawing a Square
type these commands into
the command input window,
pressing <enter> after each
command
forward 100
right 90
forward 100
right 90
forward 100
right 90
forward 100
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Error Messages

Your input:
forward 10 20

Your input:
back
error
messages
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5. More Commands

penup
 causes
the turtle to pick up its pen so that when it
moves no line is drawn

pendown
 puts
the pen back down so drawing starts again
continued
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
setpencolor <number>
 changes
the colour of the turtle’s pen
 e.g. setpencolor 5

make your turtle draw a pink line
MSW Logo has
command help
under "Index"
continued
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
clean
 clears

the turtle's drawing area
home
 moves
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the turtle back to the center of the drawing area
15
Example Using Setpencolor
forward 100
setpencolor 5
right 72
forward 100
setpencolor 14
right 72
forward 100
setpencolor 3
right 72
forward 100
setpencolor 2
right 72
forward 100
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Because the turtle
turned right
72 degrees
5 times, it made
a pentagon
16
6. The Repeat Command


Get the turtle to do things many times, by using
the repeat command.
e.g. repeat 4 [forward 10]
 move
the turtle forward 10 spaces, 4 times
 the turtle will move forward 40 spaces altogether

In general, you type:
 repeat
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<number> [ <commands> ]
17
Draw a Square with Repeat
repeat 4 [forward 100 right 90]
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Using Repeat

1.What will the following command draw?
 repeat

3 [forward 100 left 120]
2. Make a circle using the repeat command.
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Answer 1: Draw a Triangle
repeat 3 [forward 100 left 120]
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Answer 2: Draw a Circle
repeat 360 [forward 1 right 1]
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7. Procedures

Add a new command to Logo by writing a
procedure.
 to
<name of your procedure>
<command 1>
A procedure is a new
<command 2>
command, built out of
:
other commands
end
continued
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
For example:
 to
square
repeat 4 [forward 100 right 90]
end

The new command (procedure) is for drawing a
square
 it
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can be used just like other Logo commands
23
Typing in a Procedure
•A "To Mode" window
pops up after you type
to <name of procedure>
•You enter your
procedure line by line,
and type end or press
Cancel to finish.
continued
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• After typing
repeat 4 [forward 100 right 90]
end
continued
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
Executing the procedure:
 square
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A Circle Procedure

The program:
 to
circle
repeat 360 [forward 2 right 1]
end

Test it out:
 circle
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The Edall Button

To add more procedures, or change one you've
already written, click on the Edall button.
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Using Edall

Enter a procedure for drawing a purple pentagon:
 to
pentagon
setpencolor 10
repeat 5 [forward 75 right 72]
end

In the Editor "File" menu, select "Save and Exit"
when you are finished.
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A Pentagon
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Saving Procedures

If want to use the procedures some other time, you
should save them.
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8. Circle and Square

How would you write the procedure
circle_and_square to make a drawing that looks
like this?

The triangle is the
position of the turtle
at the end of the
procedure.
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Procedure
 to
circle_and_square
home
clean
repeat 360 [forward 2 right 1]
forward 50
repeat 3 [left 90 forward 100]
left 90
forward 50
end

Now change circle_and_square so it uses the
circle procedure.
continued
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A procedure calls
another procedure.
circle_and_square
calls
circle
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9. Drawing a Triangle

We want a procedure that draws a triangle with a
flat base.
start

This requires different turnings of the turtle:
3
0
9
0
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120
120
35
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10. Drawing a House

A simple house is a square with a
triangle on top of it.

After drawing the square, the turtle
must move to the start of the triangle.

After drawing the triangle, the turtle
must move back to its original position.
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Procedure Calls
square
house
calls
triangle
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11. Drawing a Checkboard

We're going to write a series of procedures that
help us make a checkboard.

A checkboard is a series of columns.
A column is a series of squares.
A square is made from 4 corners.


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Procedure Calls

I'll write four procedures, that call each other in a
chain.
checkboard
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calls
column
square
corner
41
Drawing a Corner

We want a procedure that draws a straight line,
then turns 90 degrees to the right.

to corner
forward 20
right 90
end
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Where did the Turtle Go?

hideturtle
 make
the turtle invisible
 drawing still occurs, but with no turtle

showturtle
 makes
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the turtle visible again
43
Drawing a Square with Corners

A square is four
calls to corner:
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Drawing a Column with Squares

A column is eight squares, followed by the turtle
moving back to its starting position.

After drawing a square, the turtle needs to move
up by 20 to get to the starting position for the
next square.
start
start
continued
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Drawing a Checkboard with Columns

A Checkboard is eight columns.

After drawing a column, the turtle
must move right to the starting position
for the next column.

At the end of drawing the checkboard, the turtle
should move back to the lower-left corner of the
checkboard.
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12. MSW Logo Examples
Examples/Misc/curves.lgo
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continued
49
Examples/3D/Hilbert.lgo
continued
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Examples/3D/solar.lgo
continued
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Examples/Misc/clock.lgo
continued
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Examples/Windows/calc.lgo
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