Logo Lesson 5
TBE 540-40
Fall 2004
Farah Fisher
Prerequisites
 Given a shape, use basic Logo
commands and/or a procedure to draw
the shape, with and without the use of
variables.
 Use SAVE, LOAD and POTS to
manage Logo workspaces.
 Demonstrate the use of RANDOM.
Objectives
 Put a list of words into a variable and
print any item of the list.
 Print a sentence in Logo, with and
without variables.
 Print a sentence in Logo from randomly
chosen words.
 Demonstrate use of IF and IFELSE.
 Create a Logo procedure that
demonstrates the use of recursion.
Logo Lists
 A list in Logo a set of values all stored
under the same variable name.
 Other programming languages call this
an array.
 Each value stored in the list is called
an item.
 Each item has a number, e.g., in the
list [HOT COLD DOG], item #3 is DOG.
Logo Lists
 Here is a sample of the creation of a
list within a procedure:
• MAKE “COLORS [RED GREEN BLUE]
 If you (print) PR :COLORS, all three
colors will appear.
 If you PR ITEM 2 :COLORS the word
GREEN will appear.
Logo Lists
 PR ITEM 1 + RANDOM 3 :COLORS
will display a randomly chosen word
from the list of three.
 Lists are very useful in choosing words
at random.
 MAKE “WORD1 ITEM 1 + RANDOM 3
:COLORS would put a randomly
chosen word from the list into the
variable :WORD1
Logo Lists
 Logo lists may also contain numbers.
 Here is a list of prime numbers put into a
variable called PRIME.
• MAKE “PRIME [1 2 3 5 7 11 13 17 19 23]
 What would appear if you typed this?
PR ITEM 6 :PRIME (11 would be printed,
since it is the 6th item)
 How would you choose at random from the
list? A possible command:
• MAKE “F ITEM 1 + RANDOM 10 :PRIME
Sentences in Logo
 You have seen several examples of the
PR (print) command.
 It can be used to display the value of
variables or messages.
 Next you will see how to put several
pieces of information together in a
“sentence.”
Sentences in Logo
 If you already know all the words in a
sentence, you can simply put it inside
brackets, like PR [HERE IT IS.]
 But what if you are trying to include
variables (words or numbers)?
 For example, suppose you asked
someone to enter his/her name, and
you want to print HI and the name
he/she entered.
Sentences in Logo
 The commands to ask for and get the
name would be
• PR [PLEASE TYPE YOUR NAME.]
• MAKE “NM READLIST
 If you typed PR [HI :NM] to print, you
would not get the result you want.
 PR [HI :NM] would actually display
HI :NM (rather than the actual name),
since information in [ ] is taken literally.
Sentences in Logo
 Take a look at the third line of commands:
• PR [PLEASE TYPE YOUR NAME.]
• MAKE “NM READLIST
• PR (SE [HI,] :NM)
 The SE means SENTENCE (“print as a
sentence, with spaces between the parts”).
 Notice the use of ( ) instead of [ ] . The [HI,]
is taken literally, but the :NM prints whatever
is input in the previous line.
Sentences in Logo
 Examine the following procedure:
•
•
•
•
•
TO EXCHANGE
PR [PLEASE TYPE YOUR NAME.]
MAKE “NM READLIST
PR (SE [HI,] :NM)
END
 Running the procedure:
•
•
•
•
EXCHANGE (to start the procedure)
PLEASE TYPE YOUR NAME.
MARY SMITH (entered by the user)
HI, MARY SMITH
Sentences in Logo
 Next we are going to create a
procedure that puts together sentences
from randomly chosen words.
 This procedure will (1) create lists of
words (verbs, nouns, adjectives), (2)
choose randomly from these lists, and
(3) put the randomly chosen words into
a sentence and print it.
Sentences in Logo
 We will use a sentence format like this:
• THE adjective noun verb.
• Example: THE HAPPY DOG RUNS.
 To make lists of words:
• MAKE “VERBS [RUNS HOPS SINGS]
• MAKE “NOUNS [DOG TREE CAR]
• MAKE “ADJ [HAPPY GREEN BIG]
Sentences in Logo
 To choose randomly from these lists:
• MAKE “WORD1 ITEM 1 + RANDOM 3
:ADJ
• MAKE “WORD2 ITEM 1 + RANDOM 3
:NOUNS
• MAKE “WORD3 ITEM 1 + RANDOM 3
:VERBS
Sentences in Logo
 The procedure thus far…
•
•
•
•
•
•
•
TO RANDOM.SENTENCE
MAKE “VERBS [RUNS HOPS SINGS]
MAKE “NOUNS [DOG TREE CAR]
MAKE “ADJ [HAPPY GREEN BIG]
MAKE “WORD1 ITEM 1 + RANDOM 3 :ADJ
MAKE “WORD2 ITEM 1 + RANDOM 3 :NOUNS
MAKE “WORD3 ITEM 1 + RANDOM 3 :VERBS
Sentences in Logo
 To put the words into a sentence, we will
use PR (print) and SE (sentence).
 Remember that we are trying for
• THE adjective noun verb.
 Here is the Logo printing command we will
use:
PR (SE [THE] :WORD1 :WORD2 :WORD3 [.])
Sentences in Logo
 The final version:
•
•
•
•
•
•
•
•
•
TO RANDOM.SENTENCE
MAKE “VERBS [RUNS HOPS SINGS]
MAKE “NOUNS [DOG TREE CAR]
MAKE “ADJ [HAPPY GREEN BIG]
MAKE “WORD1 ITEM 1 + RANDOM 3 :ADJ
MAKE “WORD2 ITEM 1 + RANDOM 3 :NOUNS
MAKE “WORD3 ITEM 1 + RANDOM 3 :VERBS
PR (SE [THE] :WORD1 :WORD2 :WORD3 [.])
END
Sentences in Logo
 How could you make
RANDOM.SENTENCE into a “random
story”?
 How about…
• TO RANDOM.STORY
• REPEAT 5 [RANDOM.SENTENCE]
• END
An Addition Drill
 Logo sentences can be constructed
using numbers, too.
 Suppose you are trying to make an
addition drill with random problems.
 You would have to create a procedure
that (1) chooses two random numbers,
(2) displays the addition problem, (3)
gets the answer, (4) checks to see if it
is correct, and (5) gives feedback.
An Addition Drill
 Choosing two random numbers would
look like this:
• MAKE “X 1 + RANDOM 10
• MAKE “Y 1 + RANDOM 10
 To print the problem as a sentence:
• PR (SE :X [+] :Y [= ?])
 What would be different for a
multiplication problem? For larger
numbers?
An Addition Drill
 Getting the answer would look like this:
• MAKE “ANS FIRST READLIST
 The procedure so far is…
•
•
•
•
•
TO ADD. PROBLEM
MAKE “X 1 + RANDOM 10
MAKE “Y 1 + RANDOM 10
PR (SE :X [+] :Y [= ?])
MAKE “ANS FIRST READLIST
An Addition Drill
 The next step is to check the answer.
 The question is…how will the computer
know the right answer when two
random numbers were chosen?
 The correct answer should be :X + :Y
since :X and :Y contain the chosen
numbers.
 But how will the computer compare the
student’s answer with the correct
answer?
An Addition Drill
 The IF command is part of all
programming languages.
 It asks the computer to make a judgment
about whether something is true or false.
 In this case the student’s answer will
either be the same as the computer’s or
not the same - the “equality” will either be
true (equal) or false (not equal).
An Addition Drill
 The IF statement also has to tell Logo
what to do if the judgment is true.
 In this case, we will tell Logo to print
the word RIGHT if the student’s answer
is the same as the computer’s.
 Here is the command:
• IF :ANS = :X + :Y [PR [RIGHT]]
 An explanation follows on the next
slide.
An Addition Drill





IF :ANS = :X + :Y [PR [RIGHT]]
:ANS contains the student’s answer.
:X + :Y is the correct answer
If the two are the same (equality is true),
then whatever is inside the [ ] is done.
In this case, PR [RIGHT] is inside the [ ].
Notice that one set of [ ] is for the IF
statement and the other is part of PR.
An Additional Drill
 Here’s the completed procedure.
•
•
•
•
•
•
•
TO ADD.PROBLEM
MAKE “X 1 + RANDOM 10
MAKE “Y 1 + RANDOM 10
PR (SE :X [+] :Y [= ?])
MAKE “ANS FIRST READLIST
IF :ANS = :X + :Y [PR [RIGHT]]
END
An Addition Drill
 But wait…wouldn’t it be better if we
gave them some feedback when they
didn’t get the right answer?
 There is an IFELSE statement in Logo
that allows you to tell the computer
what to do if the IF comparison is true
AND what to do otherwise.
An Addition Drill
 IFELSE comparison [actions if true]
[actions if false]
 For our procedure, it might look like
this:
 IFELSE :ANS = :X + :Y [PR [RIGHT]]
[PR [WRONG]] OR
 IFELSE :ANS = :X + :Y [PR [RIGHT]]
[PR (SE [NO, THE ANSWER IS] :X +
:Y)]
An Addition Drill
 Here it is with two kinds of feedback:
•
•
•
•
•
•
TO ADD.PROBLEM
MAKE “X 1 + RANDOM 10
MAKE “Y 1 + RANDOM 10
PR (SE :X [+] :Y [= ?])
MAKE “ANS FIRST READLIST
IFELSE :ANS = :X + :Y [PR [RIGHT]] [PR
(SE [NO, THE ANSWER IS] :X + :Y)]
• END
As Addition Drill
 One more thing…the ADD.PROBLEM
procedure prints only one problem.
 Shouldn’t a drill have more than one
problem?
 How about this…
• TO ADD.DRILL
• REPEAT 10 [ADD.PROBLEM]
• END
Recursion
 Recursion really means repetition, but
it is not the same as REPEAT.
 In Logo , it usually refers to using the
name of a procedure inside the same
procedure.
 For a detailed discussion of recursion,
see
http://www.csudh.edu/fisher/tbe540/LH
O5A.htm
Self Check Lesson 5
 What will be printed in the text window
after the commands below are entered?
 MAKE “COLORS [RED GREEN BLUE]
 PR :COLORS
 COLORS
 RED GREEN BLUE
 Depends on which color is chosen.
Self Check Lesson 5
 What will be printed in the text window
after the commands below are entered?
 MAKE “COLORS [RED GREEN BLUE]
 PR :COLORS
 COLORS
 RED GREEN BLUE
 Depends on which color is chosen.
Self Check Lesson 5
 What will be printed in the text window
after the commands below are entered?
 MAKE “COLORS [RED GREEN BLUE]
 PR ITEM 2 :COLORS
 GREEN
 RED GREEN BLUE
 Depends on which color is chosen.
Self Check Lesson 5
 What will be printed in the text window
after the commands below are entered?
 MAKE “COLORS [RED GREEN BLUE]
 PR ITEM 2 :COLORS
 GREEN
 RED GREEN BLUE
 Depends on which color is chosen.
Self Check Lesson 5
 What will be printed in the text window
if the commands below are entered?
• MAKE “DOGS [BEAGLE PIT BULL]
• MAKE “WORD2 ITEM 2 :DOGS
• PR “WORD2
 BEAGLE PIT BULL
 PIT BULL
 PIT
Self Check Lesson 5
 What will be printed in the text window if
the commands below are entered?
• MAKE “DOGS [BEAGLE PIT BULL]
• MAKE “WORD2 ITEM 2 :DOGS
• PR “WORD2
 BEAGLE PIT BULL
 PIT BULL
 PIT
{“items” are separated by a space}
Self Check Lesson 5
 What will be printed in the text window
if the commands below are entered?
• MAKE “X 27
• IF :X > 5 [PR [TOO BIG!]]
 Nothing will be printed.
 TOO BIG
 PR [TOO BIG]
Self Check Lesson 5
 What will be printed in the text window
if the commands below are entered?
• MAKE “X 27
• IF :X > 5 [PR [TOO BIG!]]
 Nothing will be printed.
 TOO BIG
 PR [TOO BIG]
Self Check Lesson 5
 What will be printed in the text window
if the commands below are entered?
• MAKE “BB 100
• IFELSE :BB > 100 [PR [yes]] [PR [no]]
 Nothing will be printed.
 yes
 no
Self Check Lesson 5
 What will be printed in the text window
if the commands below are entered?
• MAKE “BB 100
• IFELSE :BB > 100 [PR [yes]] [PR [no]]
 Nothing will be printed.
 yes
 no
{:BB=100, so it is NOT greater
than 100}
Logo Lesson 5
 Try the activities posted under Lesson
5 on the class website.