STRINGS 



Strinq variables enable a programmer to store and 
Manipulate words in a E'-ASIC program* In this Module campers 
will experiment with the various string handling features of 
the Atari* Upon completing this module, campers will be able 
to write a program that converts English to Pig Latin* 

were originally introduced in the 
If you feel you need to brush up on 
to read the following materials* 



Inside Atar i BASIC t pp* 40 - 44 
Your Atar i Computer I pp ♦ 64 - 65 

Atar i 40 0/80 Q E'-ASIC Reference Manual t pp* 37 - 40 



If you feel that any of your campers are unsure of how 
to dimension strings* you can use the accompanying worksheet 
entitled* "String Variables Worksheet*" to review 
initializing string variables* 

When you are discussing any type of variable* we 
recommend that you encourage your campers to use descriptive 
variable names* For example* NAME$ is much more meaningful 
to the reader than N$* Also* encourage your campers to 
reserve ample space for their strings in order to account for 
the largest conceivable input that may need to be stored in 
the string* String variables can be as large as you wish* as 
long as they will fit in the computer's memory* 



IE r-i <d >=c ± r-i <3 S t- ± r~i <3: ss 

Indexing strings enables you to extract or change a 
portion of a string* Isolating a portion of a string becomes 
particularly useful when strings are used to hold data* 

Explain the format and procedure for accessing a 
portion of a string using an index* Campers should 
understand the following concepts* 

1* One index in parentheses sets up a substring that 
includes the indexed element of the string to the last 
elemert of the original string* An example of using a single 
index is listed below* The program prints M LF"' on the 
screen* 



Copyright Atari* Inc* 1983* All rights reserved* 

1 

- 



String variables 
module on variables* 
strings* you may want 



INDEXING STRINGS 

< Continued ) 



DIM WORD$(10) 
WORD$ = "HELP" 
PRINT W0RD$(3) 
LP 



2* Two indices in parentheses can be used to isolate any one 
element, or a group of elements, in a string* A ssnple 
program using two indices is listed below* 



DIM WORD$<20> 
WORD* = "ATARI CAMP 
PRINT W0RD$<2,9> 
TARI CAM 

PRINT WORD$(7*10) 
CAMP 

PRINT W0RD$<2,4) 
TAR 



Acti vi ty ♦ 1 



1 « Have the csnpers type In the following progran* Canpers 
should insert their own nawe in quotes on line 40* Discuss 
what happens to the substring that is printed on the screen 
each tine the index in parentheses is incremented ♦ 



10 REM * INDEX TO A STRING 

- 20 REM 

30 DIM NAME$<30) 

40 NAME$ = "GEORGE WASHINGTON 

50 PRINT NAME$ ( 1 ) 

60 PRINT NAME*<2) 

70 PRINT NAME$ ( 3 ) 



2* Have the campers change the index* so that only the last 
letter in their name is printed on the screen* 

xxx Leave the NAMES program in memory for the next activity* 



Copyr ight 



Atari* Inc. 1983* 



All rights reserved* 



INDEXING STRINGS 

( Continued ) 



Activity *2 

This progran exenplifies how to isolate 3 substring by 
using two indices* 

1* Edit the NAME* progran currently in nenory by typing in 
the three additional lines listed below* Ask the canpers to 
predict what will be printed on the screen* 



2* Have the canpers edit the progran to print their 
initials* 



Act i v i ty *3 



1# A variable can be used in the place of an index to a 
string* For exanple* the variable COUNT represents an index 
of three in the program below* 



Using a variable enables you to change the index without 
repeating the string statement* This is particularly useful 
when you W3nt to ex tract one element of a string at a tine* 
In the progran below* canpers will print their name in big 
letters on the screen* By using a variable index* they will 
be able to print one letter of their nane at a tine* A delay 
loop holds the current letters on the screen before the next 
letter is printed* Without the delay loop it would appear as 
though all the letters were printed on the screen at the sane 



50 
60 
70 



PRINT NAME* ( 1*1) 
PRINT NAME*<1*3> 
PRINT NAME$<5*5) 



COUNT = 3 

NAME$ = "ROBERT" 

PRINT NAME$(C0UNT*6) 

BERT 



Copyright Atari* Inc* 1983* All rights reserved* 

3 



INDEXING STRINGS 

( CONTINUED ) 



tine* Note that the counter (LETTER) to the FOR ♦ ♦ ♦ Next 
loop is also used to increment the position of where the next 
letter will be printed* Have the canpers type in the program 
listed below* Be sure that they insert their own nane on 
line 140 and the number of letters in their nane on line 150* 



100 REM * VARIABLE INDEX 

110 REM * 

120 GRAPHICS 2+16 

130 DIM NAME*<20> 

140 NAME* = "JOHN JONES" 

150 LENOFNAME = 10 

160 FOR CHAR = 1 TO LENOFNAME 

170 POSITION CHAR+3*5 

180 PRINT *6;NAME$(CHAR,CHAR) 

190 FOR DELAY = 1 TO 500 * NEXT DELAY 

200 NEXT CHAR 



2* Have the caMpers experinent with printing their full nane 
on the screen, printing their nane on a diagonal • etc* 
Challenge the canpers to print the letters of their nane in 
the reverse order* This can be done by using the following 
FOR ♦ ♦ NEXT loop on line 160* 

FOR CHAR = LENOFNAME TO 1 STEP -1 



Activity *4 



1* It is also possible to alter a portion of s* string by 
using indices* In the example below* new letters are being 
assigned to the 10th through the 13th elenent of the SOUP AND 
SALAD string* Ask the canpers to predict what the program 
listed below will print on the screen* before to typing it 
into the computer* Have then RUN the progran to test their 
hypotheses ♦ 



10 REM * A SUBSTRING SWITCH 

20 REM x 

30 DIM LUNCH*(2Q> 

40 LUNCH* = "SOUP AND SALAD" 

50 PRINT LUNCH$ 

60 LUNCH* < 10 , 13) = "BREA" 

70 PRINT LUNCH* 



Copyright Atari* Inc ♦ 



1983* All rights reserved* 
4 



INDEXING STRINGS 

< Continued ) 



2 ♦ Ask the canpers to edit the progran to print SOUP A LA 
CARTE* They will need to change the indices, as well as the 
substring in line 60* 



Copyright Atari, Inc. 1983* All rights reserved* 



G c:> r* ■ «{.::: o 1:, €E* r~n -fc. il i~i <"jfc S "t i c~b «cj <b 



EI ; plain w h a t concatenatiori me a n s « W h e ri s t r i n 9 s are 
conca tena ted * they are linked together* Explain how two 
strings can be concatenated together* Discuss how it is 
possible to change a portion of a string or concatenate one 
string to another string by using indices* 



Activit y 



1* The following program is an example of how two strings 
can be concatenated to output a longer string* Call the 
campers' attention to the fact that both strings are being 
dimensioned by one DIM statement on line 30* Have the 

campers type in the program listed below* RUN the program to 
see what is printed on the screen* 



10 REM * STRING CONCATENATION 

20 REM * 

30 DIM PREFIX* ( 10 ) ,ROOT*< 10 ) 

40 PREFIX* = "TELE" 

50 ROOT* = "VISION" 

60 PRINT PREFIX*; ROOT* 



2* Now have the campers edit the program to print 
TELECOMMUNICATIONS* TELENETWORK* or TELEGRAM ♦ 



Activity *2 



1* To see how two strings can be concatenated using indices* 
have the campers type in the program listed below* 



10 REM * CONCATENATE A SUBSTRING 

20 REM * 

30 DIM ORIGINAL*< 10 ) *EXTENSION*( 10 ) 

40 ORIGINAL* = "TELEPHONE" 

50 EXTENSION* - "GRAPH" 

60 ORIGINAL* (5, 9) = EXTENSION* 

70 PRINT ORIGINAL* 



Copyright Atari* Inc ♦ 1983* All rights reserved* 

6 



1 EZ M 



Introduce the "LEN" string function ♦ The length 
function counts the nunber of characters in a string, 
including any spaces and synbols* 

Activity i 1 

1* Review the fact that a string can be assigned its 
contents fron within a program or fron a progran user ' s 
input ♦ Have the students type in the progran listed below in 
order to experiment with the LEN function* 



10 REM * THIS PROGRAM DEMONSTRATES 
20 REM * THE LEN FUNCTION 
30 REM * 

^0 DIM WORD*<20> 

50 PRINT "TYPE IN A WORD" \ 

60 INPUT WORD* 

70 PRINT "THERE ARE " J LEN ( WORD* ) J " LETTERS IN YOUR WORD* 



2» The canpers should be able to explain why there are 
seni-colons used in line 70, and why there is a space 
enclosed in quotes following the word "are" and before the 
word "letter". RUN the program* 

3* Have the students RUN the progran a second tine* This 
tine, type 5 spaces and then type the word* Use the sane 
word both tines* Ask you canpers if the progran reported the 
sane nunber of letters for the word both tines* 



xxx Leave the progran in nenory so that it can be edited in 
the next activity* 



Copyright Atari* Inc* 1983* All rights reserved* 

7 



Explain how to compare strings in BASIC* Emphasize the 
fact that the strings being compared must be identical » 
Upper and lower case letters do not natch* YES followed by a 
space does not natch a YES response with no spaces before or 
after it* 



Activity i 1 



1* The students should edit the LEN function program by 
typing in the following lines* 



20 REM * STRING COMPARISON 
40 DIM WQRD$<20 ) , ANSWER$(3) 

80 PRINT "WOULD YOU LIKE TO KNOW HOW LONG 
90 PRINT "ANOTHER WORD IS" J 
10 0 INPUT ANSWERS 

110 IF ANSWER*="YES" THEN GOTO 50 



2* Have the students RUN the program and experiment with the 
following responses* 

NO* Yes* YES * and MAYBE 



3* One way to avoid errors or confusion on the part of the 
user giving a response is to dimension ANSWERS with one 
character and ask for a "Y" or "N" response* Then the 
comparison will be made with the first letter of the response 
regardless of what the user types in* YES* YEP* and Yes will 
all be treated as "yes*" Note how ANSWERS is dimensioned to 
one character in the following program* 



Activity |2 



1* Now use indices* substrings ♦ concatenation* and LEN to 
write words in Pig Latin* Pig Latin takes the first letter 
of a word, moves it to the end of the word and adds an "ay" 
on the end* The students should fill in the missing 
information in the program listed below and type it into the 
comp uter ♦ 



Copyright Atari* Inc * 1983* All rights reserved* 

8 



10 REM * FIG LATIN 

2 0 rem * 

30 DIM WORD* < 20 ) * ANSWER** < 1 ) » GUAR* ( 1 ) 
40 PRINT " TYPE IN A WORD" J 

50 INPUT 

55 PRINT 

60 LEINGTH ■ (WORD*) 

70 CHAR* = WORD*( , ) I REM CHAR* IS ASSIGNED THE FIRST ELEMENT 

OF WORD* 

80 PRINT "THERE ARE " }" LETTERS IN YOUR WORD." 

85 PRINT 

90 PRINT WORD*(2)J ,M AY IS YOUR WORD IN PIG LATIN." 

95 PRINT 

100 PRINT "WOULD YOU LIKE TO KNOW ANOTHER WORD" 
110 PRINT "IN PIG LATIN? (TYPE Y OR N.)" 
115 PRINT 

120 INPUT 

130 IF ANSWER* = "Y" THEN GOTO 40 



Copyright Atari. Inc. 1983. All rights reserved. 

9 



I R O O R A M M X N! 13 C II I _ I E M G E S U S3 IC M G 

s t i 3: m s 



1 ♦ Write an entire Message in Pig Latin* Have a user type 
in a Message in English and you print the Message in Pig 
Latin* E'.e sure to reserve enough space in a string to input 
a very long Message, in case the user is extrenely verbose* 
Starting with the first letter of the Message, cOMpare each 
eleMent of the string to a space in order to find the break 
between each word* Each tine you encounter a space* convert 
the previous word to Pig Latin* print in on the screen* and 
read on* The following EiJASIC code May prove to be useful to 
you ♦ 



FOR LETTER ■ 1 TO LENGTH 

CHAR* = MESSAGE* (LETTER* LETTER) 

IF CHAR* <> M 11 THEN WORD* ( INDEX * INDEX ) ■ CHAR* 
INDEX = INDEX + 1 
NEXT LETTER 

PRINT WORD* (2) J * * * 



2* Devise your own secret code* Write a prograM that 
converts a Message typed into the coMputer into your secret 
code* One technique for writing a secret code is to switch 
letters for other letters in the alphabet* For exaMple* all 
the "A's" could be converted to "Z's*" Be creative* 



3* Write a prograM that juMbles up the letters in a word* 
The juMbled word is printed on the screen* The user is asked 
to guess what the word is and type the letters of the word in 
their correct order* Give the user additional guesses for 
incorrect responses* 



Copyright Atari ♦ Inc* 1983* All rights reserved* 

10 



S T Ffc X IM G S 
CAMPER COPY 



oxo String Indexing Prograns «no 



10 REIM * INDEX TO A STRING 

2 0 REIM 

30 DIM NAME:$(30) 

40 NAME* = 11 GEORGE WASHINGTON" 

50 PRINT NAME$<1) 

60 PRINT NAME:* (2) 

70 PRINT NAME$<3) 



50 PRINT NAME$< 1,1) 
60 PRINT NAME$( 1,3) 
70 PRINT NAME$(5,5) 



100 
110 
120 
130 
140 
150 
160 
170 
180 
190 
200 



REIM * VARIABLE INDEX 
REIM * 

GRAPHICS 2+16 

DIM NAME* (20) 

NAME* = "JOHN JONES" 

LENOFNAME = 10 

FOR CHAR = 1 TO LENOF r NAME 

POSITION CHAR+3,5 

PRINT *6JNAME$( CHAR, CHAR) 

FOR DELAY - 1 TO 500 : NEXT DELAY 

NEXT CHAR 



10 REM * A SUBSTRING SWITCH 

2 0 REM * 

30 DIM LUNCH$(20) 

40 LUNCH$ = "SOUP AND SALAD" 

50 PRINT LUNCH* 

60 LUNCH* CIO ,13) = "BREA" 

70 PRINT LUNCH* 



Copyright Atari, Inc* 1983* 

11 



All rights reserved* 



S T R 31 M G S3 
Canper Copy Continued 



xxxxx Concatenation ProgrsMS xxxxx 



10 REM x STRING CONCATENATION 

20 REM x 

30 DIM PREFIX* (10), ROOT* (10) 

40 PREFIX* = "TELE" 

50 ROOT* = "VISION " 

60 PRINT PREFIX* J ROOT* 



10 REM x CONCATENATE A SUBSTRING 

20 REM x 

30 DIM ORIGINAL*( 10 ) , EXTENSION* ( 1 0 > 

40 ORIGINAL* = "TELEPHONE" 

50 EXTENSION* » "GRAPH" 

60 0RIGINAL*<5,9) = EXTENSION* 

70 PRINT ORIGINAL* 



xxxxx LEN Function Prograns xxxxx 



10 REM x THIS PROGRAM DEMONSTRATES 

20 REM x THE LEN FUNCTION 

30 REM x 

40 DIM WORD*(20) 

50 PRINT "TYPE IN A WORD" i 

60 INPUT WORD* 

70 PRINT "THERE ARE " J LEN ( WORD* ) J " LETTERS IN 



YOUR WORD," 



Copyright Atari, Inc. 1983. All rights reserved. 

12 



S T r C I! t i G S 

Cstiper Copy G o n t i ft u e d 

xxxxx CoMp3ring Strings xxxxx 

20 REM x STRING COMPARISON 

80 PRINT " WOULD YOU LIKE TO KNOW HOW LONG" 
90 PRINT "ANOTHER WORD IS" J 
100 INPUT ANSWER* 

110 IF ANSWER*="YES" THEN GOTO 50 

xxxxx Pig Latin Program xxxxx 
10 REM * PIG LATIN 
20 REM * 

30 DIM WORD*(20 ) ,ANSWER*( 1 ) ,CHAR*( 1 ) 
40 PRINT "TYPE IN A WORD" J 

50 INPUT 

55 PRINT 

60 LENGTH = (WORD*) 

70 CHAR* = WORD*( , KREM CHAR* IS ASSIGNED THE FIRST ELEMENT 

OF WORD* 

80 PRINT "THERE ARE "J '," LETTERS IN YOUR WORD." 

85 PRINT 

90 PRINT W0RD*<2>; J "AY IS YOUR WORD IN PIG LATIN." 

95 PRINT 

100 PRINT "WOULD YOU LIKE TO KNOW ANOTHER WORD" 
110 PRINT "IN PIG LATIN? (TYPE Y OR N . ) " 
115 PRINT 

120 INPUT 

130 IF ANSWER* = "Y" THEN GOTO 40 



Copyright Atari, Inc. 1983. All rights reserved. 

13 



TRING VARIABLE RE VXEW 

WORKSHEET 



String variables Must first be dimensioned with a DIM 
instruction* The dimension statement determines the maximum 
number of characters which can be held in the string* 



1« Type in the following program and RUN it to see what 
happens ♦ 



10 REM x A PROGRAM TO DEMONSTRATE 

20 REM x THE DIM FUNCTION ♦ 

30 REM * 

40 DIM FRUIT*<5) 

50 FRUIT* = "APPLE" 

60 PRINT FRUIT* 



2* Note that the word being assigned to the string must be 
in quotes* If you change APPLE to BANANA * what will be 
printed on the screen? \ Try it and see* 



3* A string variable can contain any combination of letters* 

numbers* spaces* and symbols* Also* the contents of a string 

can be assigned from within a program or from input* Type in 
the following program* 



10 REM x THIS PROGRAM DEMONSTRATES 

20 REM x THE VARIOUS POSSIBLE ELEMENTS 

30 REM x OF A STRING FROM INPUT* 
40 REM x 

50 DIM TIME$(40) 

60 PRINT "WHAT TIME IT IT"; 

70 INPUT TIMES 

80 PRINT "IT'S M J TIME$J 41 ! I'M LATE! BYE*" 



3* When you are asked what time it is, type in 10:30 am* and 
RUN the program* 

5« What would be printed out if your typed in ten-thirty? 
Try it and see* 



Copyright Atari* Inc* 1983* All rights reserved* 

14 



r> nr & #. 



This nodule introduces three BASIC statements* READ* 
DATA* and RESTORE enable 3 programmer to assign values to 
variables More efficiently than the individual variable 
assignments presented thus far* Reading and storing data ar 
explained* and campers can experiment with various types of 
data* After completing this module* campers should be 
familiar with how to write versatile programs that 
systematically read data and check for the last data entry* 

Before participating in the activities in this module* 
campers must understand the difference between a numeric and 
a string variable* The participants also must have had 
experience programming SOUND on the Atari* 

If you are unfamiliar with the READ* DATA* or RESTORE 
statements* they are explained in the following books* 



Inside Atari BASIC ♦ pp* 60-63 
Your Atar i Computer * pp* 76-78 



Re-a=dl and Data 



1* In order to familiarize campers with the READ and DATA 
statements* start by writing a simple program on the board 
like this one* 



10 REM * READ DATA DEMO 

20 REM * 

30 DIM DAY*<20> 

40 NUMOFDAYS = 7 

50 PRINT 

60 FOR DAYOFWEEK = 1 TO NUMOFDAYS 

70 READ DAY* 

80 PRINT DAY* 

90 NEXT DAYOFWEEK 

100 DATA SUNDAY* MONDAY* TUESDAY 

110 DATA WEDNESDAY* THURSDAY* FRIDAY 

120 DATA SATURDAY 



2* Explain the format and function of the READ and the DATA 
statements* A READ statement enables a programmer to 
retrieve values from a list of data* 



Copyright Atari* Inc* 1983* All rights reserved* 

1 



FcEI^O bi D DATA 

( Continued ) 



The DATA st3tefient allows the programmer to store large 
quantities of data ef f iciently ♦ Note that each elenent of 
data is separated by a comm3* Even though we are assigning a 
word to the string variable DAY*, no quotation Marks are 
needed in the list of data* 

3* Explain that the READ statement looks for the first 
■•unread" eleMent of data* The concept of a "pointer" should 
be explained here* The conputer Maintains a pointer that 
points to the next data iteM to be READ* Each tine an 
eleMent of data is read* the pointer is advanced to the next 
eleMent of data* 

4* READ stateMents are custoMarily used in a loop* In this 
exaMple* we are using a FOR ♦ ♦ NEXT loop* When a FOR ♦ ♦ 
NEXT loop is used* the nunber 'of tiMes the loop is to be 
executed Must correspond to the quantity of data* If a READ 
statenent is executed and all of the data has been read* you 
will get an error Message* 

5* Step through the prograM and execute each instruction 
just as the coMputer would* Write each DAY* on the board as 
you execute the PRINT DAY* instruction* Each tiMe an eleMent 
of data is read* the "pointer" is advanced to the next data* 
Use your pencil to point to the data to be read as you step 
through the prograM* Call the caMpers' attention to the fact 
that data can appear on More than one line* The coMputer's 
pointer autoMatical ly advances to data on the next line* 
DATA lists are always read in the order of their line nuMber * 
froM the lowest to the highest* 



Activity *1 



1* Have the caMpers type in the days of the week prograM 
listed below* 

• 

10 REM * READ DATA DEMO 

20 REM x 

30 DIM DAY*<20> 

40 NUMOFDAYS = 7 

50 PRINT 

60 FOR DAYOFWEEK = 1 TO NUMOFDAYS 

70 READ DAY* 

80 PRINT DAY* 

90 NEXT DAYOFWEEK 

100 DATA SUNDAY, MONDAY, TUESDAY 

110 DATA WEDNESDAY, THURSDAY, FRIDAY 

120 DATA SATURDAY 



Copyright Atari, Inc. 1983. All rights reserved. 

2 



FC EI iAi D 



At M D DATA 

( Continued ) 



2« Cafipers should RUN the progran to see what is printed on 
the screen* Have the campers change the NUMQFDAYS assignment 
to NUHOFDAYS m 2* RUN the program again to see what happens* 
Then have the campers assign 8 days to the NUMOFDAYS 
variable* Once again* RUN the program to see what happens* 



Activity * 2 



1* A conditional statement* such as IF ♦ ♦ THEN* also can be 
used to set up a loop to read data* A GOTO* intructs the 
computer to re-execute a set of instructions until the IF * ♦ 
THEN condition is met* The IF ♦ ♦ THEN statement searches 
for the "flag" at the end of the list of data* The flag is 
an unlikely element of data that has been placed at the end 
of the data list to indicate that there is no more data* The 
IF ♦ ♦ THEN statement checks each element of data that is 
READ and when the flag is encountered* the loop is 
terminated* In the following activity* the word "FINISH" has 
been placed at the end of the list of days to serve as a 
f lag* 



210 DATA SATURDAY * 7TH * FINISH 



When FINISH is READ* the program ends* You may want to 
take this opportunity to point out to the campers that using 
a conditional statement with a "flag" makes a program more 
versatile* The data can be changed or replaced with another 
set of data* and the program will still work* as long as the 
flag is the last element of data* 



2* More than one variable can be READ from a list of data* 
The program below shows how two string variables can be 
assigned values from the same DATA statement* Explain to the 
students that the pointer continues to advance to the next 
element of data each time a READ instruction is executed* 
regardless of which variable is being assigned a value* Have 
the campers type in the program listed below in order to 
experiment with the instructions* This time* a conditional 
loop is used with a flag* 



Copyright Atari* Inc* 1983* All rights reserved* 

3 



t^t-to r> x 

( Cont i nued ) 



100 REM * TWO STRING VARIABLES 

110 REM * 

120 DIM DAY*<15> ,ORDER*<10> 

130 PRINT 

140 READ DAY* 

150 IF DAY* 5 *" FINISH" THEN END 

160 READ ORDER* 

170 PRINT DAY*?" IS THE " i ORDER* J " OF THE WEEK." 

180 GOTO 140 

190 DATA SUNDAY, 1ST, MONDAY, 2ND. TUESDAY, 3RD 

200 DATA WEDNESDAY, 4TH, THURSDAY, 5TH, FRIDAY, 6TH 

210 DATA SATURDAY, 7TH, FINISH 

220 END 

If the campers' output from this prograM looks odd, 
remind then to check their spacing on line 170* 

Note that when DAY* was compared with the FINISH flag on 
line 150, FINISH was in quotes* When a string is compared 
with a word, the word Must appear in quotes* Have the 
campers type " .FINISH" at the end of line 190* Line 190 
should look like this after it has been edited* 

190 DATA SUNDAY, FIRST, MONDAY, SECOND, TUESDAY, THIRD, FINISH 

Ask then to predict what the program will print before 
RUNing it* Then insert a space before the word FINISH on 
line 190 and see what happens* 

190 DATA SUNDAY, FIRST, MONDAY, SECOND, TUESDAY, THIRD, FINISH 

t 

Ask the campers to explain why "FINISH" did not end the 
program this time* 



Copyright Atari, Inc. 1983* All rights reserved* 



FCEI^O AND DAT" A 

< Continued ) 



Activity *3 



READ stateMents can be used to assign values to nuneric 
variables as well* In fact, one DATA list can hold both 
nuweric and string data* Ask the canpers to type in the 
prograM listed below* Each canper should list the nanes of 
each Member in his or her family and the person's age* 
separated by coMhas* on line 190-200* 

Since there is no way of knowing how Many people there 
are in each caMper's fanily and therefore no way of knowing 
how Much data will be listed on lines 190-200* a different 
kind of loop for reading the data is used* This tine the 
TRAP instruction is used. Before to beginning the READ ♦ ♦ 
DATA loop, a TRAP is set to avoid an M 0UT OF DATA 11 error 
Message* When the READ stateMent on line 150 is executed* if 
there is no data left* ordinarily the prograM would stop and 
you would get an error Message* By using the TRAP 210 
instruction* we can trap that error and redirect the coMPuter 
to continue with the instruction listed on line 210* Explain 
this third Method of reading data, and have the caMpers 
experiMent with the prograM listed below* 



100 REM x TRAPPED DATA 

110 REM * 

120 DIM PERSQN*<20> 

130 PRINT 

140 TRAP 210 

150 READ PERSON* 

160 READ AGE 

170 PRINT PERS0N$; M IS *JAGET* YEARS OLD ♦ 11 

180 GOTO 140 

190 DATA MARGIE * 47 * JOHN ♦ 50 ♦ BETH * 12 

200 DATA 

210 END 



Copyright Atari* Inc* 1983* All rights reserved* 

5 



RESTORE 



Activity *1 



READ and DATA statements are commonly and quite 
conveniently used to play music on the Atari ♦ The values for 
the voice, pitch, distortion, and/or loudness of the note can 
be stored as DATA and read as the tune is played* In this 
activity the RESTORE command is introduced in a program that 
plays music* Campers will use the RESTORE instruction to 
reset the pointer to the beginning of a list of SOUND data, 
so that the tune will be replayed* 

Explain the RESTORE instruction to the campers* RESTORE 
resets the data pointer back to the first element of DATA 
listed in the program* (It is also possible to give a line 
number in the RESTORE instruction in order to redirect the 
pointer to a specific set of DATA* This will be discussed in 
the next activity*) 

You also may need to briefly review the four components 
of the SOUND command* In the following program four values 
are being READ from DATA: PITCH, DISTORTION, LOUDNESS, and 
TIME* TIME indicates the length of the delay between each 
note* The voice is always zero* A minus one is used as a 
flag at the end of the DATA* 

Have the campers type in the program listed below* 



100 REM * MUSIC 

110 REM * 

120 READ PITCH, DISTORT, LOUD, TIME 

130 IF TIME - -1 THEN GOTO 210 

140 SOUND 0, PITCH, DISTORT, LOUD 

150 FOR DELAY = 1 TO TIME t NEXT DELAY 

160 GOTO 120 

170 DATA 121,10,10,40,91,10,10,37 

180 DATA 0,0,0,3,91,10,10,40,108,10,10,28 

190 DATA 0,0,0,2,108,10,10,10,91,10,10,30 

200 DATA 108,10,10,10,121,10,10,80,0,0,0,0,-1 

210 END 



Note that the three variables being read can be listed 
with one READ instruction on line 120* RUN the program to 
hear the little tune* 



Copyright Atari » Inc« 1983* All rights reserved. 

6 



restore: 

( Continued ) 



Explain how to insert the RESTORE instruction on line 
130 in order to repeat the tune* The edited fornat for line 
130 appears below* 

130 IF TIME = -1 THEN RESTORE: GOTO 120 

RUN the edited program* To stop the prograM and turn 
off the sound* you Must press SYSTEM RESET because the 
progran is in an infinite loop* After this activity* you nay 
never want to teach the READ* DATA* and RESTORE instructions 
using Music in a classrooM with 12 coMputers again* 



Activity *2 



This next activity gives the caMpers an opportunity to 
experiwent with a More lengthy prograM that uses the READ* 
DATA* and RESTORE stateMents* 

Explain to the caMpers that READ and DATA stateMents can 
go anywhere in a prograM* If the prograM is quite short* or 
if there is only one set of data used repeatedly froM various 
places in the prograM* we reconnend that the DATA be placed 
at the end of the prograM* Otherwise* the DATA should follow 
soon after the READ stateMent for prograM clarity* 

Giving the DATA line nunber in the RESTORE coMMand 
enables the prograMMer to dictate which part of the data the 
pointer will be restored to* So if a RESTORE instruction 
reads* RESTORE 400* the data pointer is reset to the first 
eleMent of data appearing on line 400* 

The following prograM is the beginning of an interactive 
art show* The person using the prograM selects froM a list 
of snail pictures to Make a scene on the screen* The prograM 
uses the READ and DATA stateMents to draw the little pictures 
on the screen* The coordinates for each iMage are stored in 
separate DATA lists* The READ stateMent reads each set of 
coordinates to be used by the DRAWTO instruction on line 
270* This is a very efficient way of storing coMputer 
illustration data* The RESTORE instruction is critical in 
this prograM* Once a shape has been selected by the prograM 
user* the RESTORE instruction is used to set the data 
pointer to the specific set of coordinates needed to draw the 
shape * 



Copyright Atari* Inc* 1983* All rights reserved* 

7 



F"C E S T O Fx E 
( Continued ) 



Note how the RESTORE command is used to control which 
list of data is being READ* 

Since the READ statement on line 250 reads both X and Y, 
two flags are required at the end of the list of DATA* 
Otherwise the READ statement on line 250 will continue to 
look for DATA for Y before it will check for the flag on line 
260* If there is no More DATA left, you will get an Out of 
DATA Error* 



Ask the campers to explain why a TRAP instruction cannot 
be used to end the READ loop in lines 230 or 280* Have the 
campers predict what would happen if the line numbers were 
removed from the RESTORE commands in lines 150-170 ♦ 



Copyright Atari, Inc* 1983* All rights reserved* 

8 



RESTORE 

( Continued) 



100 REM x ART SHOW 
105 REM x 

110 MENU=90 0:REM MENU LINE NUMBER 
115 GRAPHICS 7 t COLOR 3 
120 REM x 

125 REM xxxxx MAIN LOOP xxxxx 

130 GDSUB MENU 

140 INPUT RESPONSE 

150 IF RESP0NSE<1 OR RESPONSES THEN 140 

160 IF RESPONSES THEN RESTORE 500 

170 IF RESP0NSE=2 THEN RESTORE 600 

180 IF RESPONSES THEN RESTORE 700 

190 IF RESPONSES THEN RESTORE 800 

200 REM x 

210 REM xxxxx DRAW ROUTINE xxxxx 

220 REM x 
230 READ X,Y 

240 plot x,y:rem PICTURE START POINT 

250 READ X,Y:REM GET DRAWTO DATA 
260 IF X=-l THEN 130JREM THE FLAG? 
270 DRAWTO X,Y 

§GOTO 250JREM GET MORE DATA 
REM x 
REM xxxxx MOUNTAIN xxxxx 

510 REM x 

520 DATA 0,26,12,20,20,23,30,18,35,12,42,13,45, 10,58,6 
530 DATA 62,3,70,1,82,3,90,8,102,20,112,26,120,23 
540 DATA 130,38,135,36,150,43,-1,-1 
550 REM x 

600 REM xxxxx BARN xxxxx610 REM x 

610 REM x 

620 DATA 43,50,43,46,47,46,47,50,40,50 

630 DATA 40,44,45,41,50,44,50,50,40,50,-1,-1 

64 0 REM x 

700 REM xxxxx STAR xxxxx 

710 REM x 

720 DATA 128,10,127,11,126,11,127,12,126,13,127,13,128,14,129,13 
730 DATA 130,13,129,12,130,11,129,11,128,11,128,14,-1,-1 
740 REM x 

800 REM xxxxx HORSE xxxxx 

810 REM x 

820 DATA 52 , 47 , 54 , 46 , 54 , 45 , 54 , 50 , 54 , 48 , 57 , 48 , 58 , 47 , 57 , 48 , 57 , 50 , -1 , -1 
90 0 REM x 

910 REM xxxxx MENU xxxxx 
920 REM x 
930 PRINT 

940 PRINT "1. MOUNTAIN 3. STAR" 

9Mk PRINT "2. BARN 4. HORSE" 

PRINT "WHICH PICTURE (1, 2, 3, OR 4) "J 
970 RETURN 



Copyright Atari, Inc. 1983. All rights reserved. 

9 



PROGRAMMING CHALLENGES U <3 HI M G 
READ * OA T A #. AMD RESTORE 



It Write 3 progrsM that lists the necessary values for a 
song in DATA statements* Use the RESTORE command to repeat 
the chorus of the song in between the verses* 



2. Add pictures to the ART SHOW program* 



3* Set up a PLOT subroutine like the DRAWTO subroutine in 
the ART SHOW program* Add a plotted image to the list of 
pictures one can put on the screen* For example* offer to 
draw stars and PLOT tiny dots in the sky using READ and DATA 
statements* 



Allow the user to draw the shapes anywhere on the screen* 
For example* when a person selects the barn* ask for the 
coordinates of the cabin's location on the screen* Be sure 
to tell the user the range of possible coordinates when 
asking for INPUT* Then add the person's coordinates to the 
DATA coordinates in the DRAWTO statement (DRAWTO 
X+XCOQR* Y+YCOOR) ♦ This way the person can put as many barns 
on the screen as he or she wants as well as put them anywhere 
in the picture* 



5* Draw the shapes in different colors* Store the color of 
the shape as the first element of the shape data* READ the 
value into the COLOR instruction before drawing the image* 



6* Experiment with combining different graphic modes* 
colors* sounds* etc* into a little show using the READ* DATA* 
and RESTORE statements* 



Copyright Atari* Inc* 1983* All rights reserved* 

10 



Fv FZ A O , DATA ^ AND RESTORE 

CAMPER COPY 



xxxxx Read DATA Deno xxxxx 



10 REM * READ DATA DEMO 

20 REM x 

30 DIM DAY*<20> 

40 NUMOFDAYS = 7 

50 PRINT 

60 FOR COUNTER = 1 TO NUMOFDAYS 
70 READ DAY* 
80 PRINT DAY* 
90 NEXT COUNTER 

100 DATA SUNDAY, MONDAY, TUESDAY 

110 DATA WEDNESDAY > THURSDAY, FRIDAY 

120 DATA SATURDAY 



xxxxx READ Two String Variables xxxxx 



100 REM x TWO STRING VARIABLES 

110 REM x 

120 DIM DAY*<15) ,ORDER*<10> 

130 PRINT 

140 READ DAY* 

150 IF DAY*="FINISH" THEN GOTO 220 

160 READ ORDER* 

170 PRINT DAY* J " IS THE "J ORDER* J" OF THE WEEK." 

180 GOTO 140 

190 DATA SUNDAY, FIRST, MONDAY, SECOND. TUESDAY, THIRD 

200 DATA WEDNESDAY, FOURTH, THURSDAY, FIFTH, FRIDAY, SIXTH 

210 DATA SATURDAY, SEVENTH, FINISH 

220 END 



190 DATA SUNDAY, FIRST, MONDAY, SECOND, TUESDAY, THIRD, FINISH 



190 DATA SUNDAY, FIRST, MONDAY, SECOND, TUESDAY, THIRD, FINISH 

T 



Copyright Atari, Inc. 1983. All rights reserved. 

11 



READ ^ DATA* AND RESTORE 

CAMPER COPY CONTINUED- 



xxxxi Trapped DATA xxxxx 



100 REM * TRAPPED DATA 

110 REM * 

120 DIM PERSON* (20) 

130 PRINT 

140 READ PERSON* 

150 TRAP 210 

160 READ AGE 

170 PRINT PERSON* J " IS " > AGE J " YEARS OLD," 

180 GOTO 140 

190 DATA MARGIE, 47, JOHN, 50, BETH, 12 

200 DATA 

210 END 



xxxxx Music xxxxx 



100 REM x MUSIC 



110 REM x 

120 READ PITCH, DISTORT, LOUD, TIME 

130 IF TIME ■ -1 THEN GOTO 210 

140 SOUND 0, PITCH, DISTORT, LOUD 

150 FOR DELAY = 1 TO TIME 5 NEXT DELAY 

160 GOTO 120 

170 DATA 121,10,10,40,91,10,10,37 

180 DATA 0,0,0,3,91,10,10,40,108,10,10,28 

190 DATA 0,0,0,2,108,10,10,10,91,10,10,30 

200 DATA 108,10,10,10,121,10,10,80,0,0,0,0,-1 

210 END 



Copyright Atari, Inc. 1983. All rights reserved. 

12 



F C E: t-'-i O , O/^TA^ t^t It H> RESTORE 

CAMPER COPY CONTINUED 



100 REM x ART SHOW 
105 REM x 

no menu=?oo:rem menu line number 

115 GRAPHICS 7 * COLOR 3 
120 REM x 

125 REM xxxxx MAIN LOOP xxxxx 

130 GOSUB MENU 

140 INPUT RESPONSE 

150 IF RESP0NSE<1 OR RESPONSES THEN 140 

160 IF RESPONSES THEN RESTORE 500 

170 IF RESP0NSE=2 THEN RESTORE 600 

180 IF RESP0NSE=3 THEN RESTORE 700 

190 IF RESPONSES THEN RESTORE 800 

200 REM x 

210 REM xxxxx DRAW ROUTINE xxxxx 

220 REM x 
230 READ X,Y 

240 PLOT X,Y:REM PICTURE START POINT 
250 READ X,Y:REM GET DRAWTO DATA 
260 IF X=-l THEN 130 J REM THE FLAG? 
270 DRAWTO X,Y 

4B0 GOTO 250 : REM GET MORE DATA 
|0 REM x 
00 REM xxxxx MOUNTAIN xxxxx 

510 REM x 

520 DATA 0,26,12,20,20,23,30,18,35,12,42,13,45,10,58,6 
530 DATA 62,3,70,1,82,3,90,8,102,20,112,26,120,23 
540 DATA 130,38,135,36,150,43,-1,-1 
550 REM x 

600 REM xxxxx BARN xxxxx610 REM x 

610 REM x 

620 DATA 43,50,43,46,47,46,47,50,40,50 

630 DATA 40,44,45,41,50,44,50,50,40,50,-1,-1 

640 REM x 

700 REM xxxxx STAR xxxxx 

710 REM x 

720 DATA 128, 10 ,127, 11 , 126, 11 , 127 , 12 , 126 , 13 , 127 , 13 , 128 , 14 , 129 , 13 

730 DATA 130,13,129,12,130,11,129,11,128,11,128,14,-1,-1 
740 REM x 

800 REM xxxxx HORSE xxxxx 

810 REM x 

820 DATA 52,47,54,46,54,45,54,50 ,54,48,57,48,58,47,57,48,57,50,-1 
90 0 REM x 

910 REM xxxxx MENU xxxxx 
920 REM x 
930 PRINT 

940 PRINT "1. MOUNTAIN 3* STAR" 

tO PRINT "2, BARN 4. HORSE" 

0 PRINT "WHICH PICTURE (1, 2, 3, OR 4) "} 
970 RETURN 



Copyright Atari, Inc. 1983. All rights reserved. 

13 



fZT" III" jHS. "'v" CZt 



Arrays enable s progranfier to store and Manipulate large 
quantities of information systematically and efficiently* 
Arrays are one of the more complex features of Atari BASIC* 
and it may take some practice for your campers to fully 
understand them* You may find that you need to spend time 
drawing representations of arrays and stepping through 
programs on the board more than you have in previous modules* 
One objective of this module is to help campers to recognize 
programming problems that are well-suited to using an array* 
In this module the campers will use an array to reverse the 
order of a list of numbers and to write and store a musical 
tune* 

To do this module you will need a chalk board or large 
pieces of chart paper and felt tip pens to map out arrays* 

If you feel unsure of how to use an array in a program 
or you would like to see more examples of arrays* you may 
want to look over the following references* 



ATARI 4Q0/80Q E'.ASIC Reference Manual: pp* 3* ^1-^3 
Inside Your Atari* pp* 66-7^ 
Your ATARI Computer* pp 65-67 

An array can be thought of as a series of boxes* each of 
which holds one numeric value* The following is an example 
of an array* 

i i 

I 2 I 

l_„l 
161 | 

r?~i 
i„_i 

133 I 

l„_l 
I 0 | 



An array is a group of numeric variables that have 
something in common* The values in the array* for example* 
can be students' scores on a test or the number of raffle 
tickets each teacher sold for the school bake sale* Once you 
have stored the values in an array* you can do all kinds of 
calculations on the numbers* 



Copyright Atari* Inc» 1983* All rights reserved* 

1 



ARRAYS 

(Continued) 



An array of swiMMers' tines in a race could be called 
SWIMMER* Each nunber in the SWIMMER array is called an 
"element" of the array* An index is used to identify which 
elefient of the SWIMMER array or which swinMer you are 
referring to* For exaMple* in the array below* SWIMMER(l) 
swan the race in three Minutes* SWIMMER(^) took five 
Minutes ♦ 



SWIMMER(l) 
SWIMMER(2) 

SHIMMER ( 3 ) 
SWIMMERS) 



I 3 | 

I I 

I 4 I 

I I 

I 6 | 

I I 

I 5 | 



Just as we Must reserve space in MeMory for a string* 
MeMory Must be reserved for an array* You use the DIM 
stateMent to dimension the m a x i m u m nuMber of boxes or 
elenents your array could possibly need* DIM SWIMMER<25) 
enables the prograMMer to store up to 25 eleMents or swiM 
tines in the SWIMMER array* 



DIM SWIMMERC25) 




SWIMMER(l) 
SWIMMER < 2 ) 
♦ 

SWIMMER ( 10 ) 

♦ 
♦ 

SWIMMER(20) 

♦ 

SWIMMERC25) 



As long as there is sufficient rooM in MeMory* there i 
no restriction on the size of an array that can be stored* 



Copyright Atari, Inc* 1983* All rights reserved* 



ARRAYS 

< Continued ) 



Values are stored in an array by specifying the nawe of 
the array and the index of the element* For example ♦ 
SWIMMER<1)=3 assigns a value of 3 to the first element of the 
SWIMMER array or swinner nunber one* SWIMMERC3) = 6 assigns 
a 6 to the third element of the SWIMMER array, swinner nunber 
three ♦ 



SWIMMER(l) 
SWIMMER(2) 
SWIMMER(3) 
SWIMMERS) 



I 3 | 

I I 

I 4 I 

I I 

I 6 | 

I I 

I 5 I 



The index to an array can contain a numeric value or 
variable nane* For exanple* the third element of the SWIMMER 
3rray is assigned a 6 in the code below as well* 



NUM ■ 3 

SWIMMER<NUM)=6 



Using a variable index is particularly useful when a FOR 
♦ ♦ NEXT loop is used to initialize an array* To 
inititial ize an array you usually want to fill it with zeros* 



FOR ELEMENT = 1 TO MAXELEMENTS 
SWIMMER (ELEMENT) - 0 
NEXT ELEMENT 



Activity *1 



1« Begin by explaining an array as a series of boxes, as was 
Just explained in the introduction to this Module* Drawing 
the boxes on the board is helpful when arrays are being 
introduced* Explain what an index is and how it is used to 
identify one element of an array* The fornat for the DIM 
statement of an array also will need to be explained* 



Copyright Atari, Inc* 1983* All rights reserved* 

3 



ARRAYS 

< Continued) 



2* Draw an array on the board that will hold five nufibers* 
like the one below* 



NUMBER < 1 ) =25 > NUMBER ( 1 ) 



NUMBER(2)=11Q > NUMBER (2) 



NUMBER (3) 
NUMBER ( 4 ) 



NUMBER < 5) 



Ask cahpers to suggest the numbers to be stored in the 
array* Assign the value to the element of the array 
(NUMBER(3)=98) before filling the box in the array* 



3* Ask the cawpers how they night go about printing one of 
these values in the array on the screen* Write out the 
cownand on the board as it is given* For example* PRINT 
NUMBER ( 1 ) or PRINT NUMBER < 2 ) ♦ Be sure the csMpers understand 
the difference between PRINT 2 and PRINT NUMBER < 2 ) ♦ 



Explain that a variable nane can be used as an index to 
an array* as was explained in the introduction to this 
Module* Denonstrate the use of a variable as an index when 
using a FOR ♦ ♦ NEXT loop to PRINT out all of the elements of 
an array* A sanple listing of the code appears below* 



MAXNUMS = 5 

FOR ELEMENT = 1 TO MAXNUMS 
PRINT NUMBER (ELEMENT) 
NEXT ELEMENT 



Write this subroutine on the board alongside a series of 
boxes holding the elements of the NUMBER array* Step through 
the subroutine t printing each nunber on the board as the 
PRINT NUMBER (ELEMENT) statement is executed* 



Copyright Atari, Inc* 1983* All rights reserved* 



25 



110 



ARRAYS 

( Continued ) 



5* Given the FOR ♦ ♦ NEXT loop above to PRINT the numbers on 
the screen, ask the calipers how they could program the 
computer to PRINT the numbers in the reverse order* A FOR ♦ 
♦ NEXT loop like the following should evolve from the campers 
suggestions* 

FOR ELEMENT = MAXNUMS TO 1 STEP -1 
PRINT NUMBER (ELEMENT ) 
NEXT ELEMENT 



Encourage the campers to use descriptive variable names* 
Again* step through the program* PRINTing the numbers that 
would be output on the board* 



If you think your campers are catching on to arrays and 
variable indices* proceed with the next activity* Otherwise* 
review the previous examples* using a different Brra^ name 
and new data* 



Copyright Atari* Inc* 1983* All rights reserved* 



ARRAYS 

( Continued ) 



Activity *2 



1. In this activity the campers will gradually enter a 
program that INPUTs five numbers* stores them in an array* 
PRINTs them on the screen* and then PRINTs them in the 
reverse order* Note that the variable MAXNUMS can be used to 
DIMension the array* Have the campers type in the following 
program ♦ 



100 REM * ARRAY OF NUMBERS 

110 REM * 

120 MAXNUMS = 5 . REM MAXIMUM NUMBERS WHICH CAN BE INPUT 

130 DIM NUMS(MAXNUMS) 

140 REM * 

150 REM * FILL ARRAY 

160 REM * 

170 FOR COUNT = 1 TO MAXNUMS 

180 PRINT "TYPE IN A NUMBER", 

190 INPUT VALUE 

200 NUMS(COUNT) = VALUE « REM STORE INPUT VALUE IN ARRAY 

210 NEXT COUNT 



Ask the campers to add a line at the end of the program 
to PRINT the first element of the array* Add another line 
that PRINTs the last number in the array* using MAXNUMS as 
the index to the NUMS array. 



2. Have the campers type in the following lines as a 
continuation of the Array of Numbers program* Jhe following 
lines PRINT the entire sequence of numbers in the array. RUN 
the program. 



22 
23 

24 
25 
26 
27 
28 
29 
30 
31 
32 



PRINT NUMBERS IN ORDER 



0 REM * 

0 REM * 

0 REM * 

0 PRINT 

0 PRINT 

0 PRINT 

0 PRINT 

0 FOR COUNT = 1 TO MAXNUMS 

0 PRINT NUMS(COUNT) ," "* .REM PRINT VALUE 

0 NEXT COUNT 

0 PRINT 



"YOU TYPED IN THE NUMBERS IN THE" 
"FOLLOWING ORDERt" 



+ SPACES 



Copyright Atari, Inc. 1983. All rights reserved. 

6 



iz> cri" a y dt 

( Continued ) 



3* E'.ased on what the campers know, ask then to complete the 
following lines, which print the numbers in the array in the 
reverse order ♦ 



330 REM * 

340 REM * PRINT NUMBERS IN REVERSE ORDER 

350 REM * 
360 PRINT 

370 PRINT 11 YOUR NUME'.ERS IN THE REVERSE ORDER ARE ♦ 11 
380 PRINT 

390 FOR COUNT = TO STEP 

400 PRINT < )l" N * f 

410 NEXT 

420 PRINT 
430 END 



The campers should RUN the program to see if it does wha 
they intended* 



Activity *3 



1* This next activity demonstrates additional uses of an 
array* Once again, the program INPUTs numbers* This time* 
the numbers are used as the PITCH for a SOUND command* The 
person using the program can create a little tune* Start by 
discussing the program with the campers* 



2* First* pose the question* "Suppose you wanted to use an 
array to write a tune* What instruction must appear in the 
program before the computer will allow you to use an array?" 
(Answert DIM TUNE ( ??? ) ) When you get the appropriate 
answer* draw an array of boxes on the board alongside the 
dimension statement* 



Copyright Atari, Inc* 1983* All rights reserved* 

7 



ARRAYS 

< Continued ) 



3* Now explain that as a prograMMer you want to INPUT the 
numbers that will serve as the values for the PITCH in the 
SOUND cofifisnd* You want to store the PITCH values in an 
array in order to play back the tune for the program user ♦ 
List the following INPUT code and ask the csMpers to explain 
what it does* 



100 REM * SOUND NITH AN ARRAY 

110 REM * 

120 DIM TUNE(IOO) 

130 XNOTE = 0 

140 INPUT PITCH 

150 IF PITCH = -1 THEN NUMNOTES = XNOTE ♦ GOTO 200 

160 XNOTE ■ XNOTE + 1 

170 TUNE ( XNOTE ) ■ PITCH 

180 GOTO 140 



The Minus one serves as a flag, indicating that the 
l3st note of the tune has been entered* Using a flag enables 
the user to enter as Many notes as he or she wishes* The 
user Must be told to type in a Minus one as a flag for the 
last note of the tune* The INPUT instruction is in a loop that 
continually checks for the Minus one flag* Explain to the 
caMpers that XNOTE is used instead of NOTE because NOTE is a 
reserve word* NUMNOTES is assigned the total number of notes 
typed in* Step through the INPUT routine a few tiMes and 
place soMe INPUT values in the box array you drew beside the 
DIM stateMent* 



4* Now that the notes are stored in the TUNE ajpray* we need 
to write the BASIC routine which will play the tune* The 
idea here is to get the caMpers to generate the code froM 
your English description of the prograM* To play the tune* 
the routine Must use each of the elenents of the array in the 
SOUND coMMand* Ask what would be an efficient way to use 
each value in the SOUND instruction* Establish a FOR loop 
using the sane variable nattes as were introduced in the INPUT 
routine* 

FOR NUM = 1 TO XNOTE 

In this exaMple use voice zero in the SOUND coMMand and 
use ten for both the distortion and loudness for all of the 
notes* Thus* use the following SOUND coMMand: 

SOUND 0*TUNE<XNOTE) *10*10 



Copyright Atari* Inc* 1983* All rights reserved* 

8 



ARRAYS 

( Continued ) 



You Might give the canpers the SOUND cor-mand* but leave 
out the TUNE < XNOTE ) and ask the canpers what they would 
insert* 

In order to distinguish the notes* you need a delay loo 
after playing each note* 

■ 

FOR DELAY = 1 TO 10 t NEXT DELAY 

When the loop ends, the SOUND Must he turned off before 
leaving the subroutine, < SOUND 0,0,0,0) 



200 REM x 

210 REM x PLAY TUNE 

220 REM x 

230 FOR XNOTE = 1 to NUMNOTES 

240 SOUND 0,TUNE(XNOTE) ,10,10 

250 FOR DELAY = 1 TO 10 J NEXT DELAY 

260 NEXT XNOTE 

270 SOUND 0,0,0,0 



5. Have the campers type in the entire SOUND WITH AN ARRAY 
progran which you have just worked through* RUN the prograM 
and experinent with different notes* 



100 REM x SOUND WITH AN ARRAY PLUS PLAY TUNE 

110 REM x 

120 DIM TUNE(IOO) 

130 XNOTE = 0 

140 INPUT PITCH 

150 IF PITCH = -1 THEN NUMNOTES = XNOTE. GOTO 200 

160 XNOTE ■ XNOTE + 1 

170 TUNE(XNOTE) = PITCH 

180 GOTO 140 

200 REM x 

210 REM x PLAY TUNE 

220 REM x 

230 FOR XNOTE = 1 to NUMNOTES 

240 SOUND 0 ,TUNE(XNOTE) ,10,10 

250 FOR DELAY = 1 TO 10 : NEXT DELAY 

260 NEXT XNOTE 

270 SOUND 0,0,0,0 



Copyright Atari, Inc. 1983. All rights reserved. 

9 



ARRAYS 

( Continued ) 



6* To see how the same BASIC code with 3 Menu and a few 
extra PRINT statements can work, have the campers look over 
the listing of the SOUNDARY program on their arrays 
worksheets* Note how labels have been assigned to the 
beginning line numbers of the different subroutines in lines 
170-200 ♦ Each subroutine is "called" from the main loop* 



7* Note that the third option on the menu is "LIST THE 
NOTES*" Have the campers look over lines 900*960* This FOR 
♦ ♦ NEXT loop will PRINT the values stored in the array on 
the screen* 



The PRINT statement in line 9^0 needs to be given 
careful explanation* Have the campers RUN the SOUNDARY 
program to see how it works* Take a few minutes to 
experiment with entering different tunes* 



930 

9^0 
950 
960 



FOR XNOTE = 1 TO NUMNOTES 
PRINT "TUNE( " J XNOTE J " ) 11 J 11 
NEXT XNOTE 
RETURN 



;tune<xnote) 



Copyright Atari, Inc* 1983* All rights reserved* 

10 



100 REM x SOUND ARRAY 

110 REM x 

120 REM x BOUNDARY 
^| REM x INITIALIZE VARIABLES AND ARRAY 
^T- REM x 

150 DIM TUNE(IOO) 
160 XNOTE=0 

165 REM x ASSIGN LABELS TO LINE NUMBERS 
170 MENU=300 
180 VALUES=500 
190 PLAY=700 
200 NUMBERS=900 
210 REM x 

220 REM x MAIN LOOP 

230 REM x 
240 GOSUB MENU 
250 INPUT RESPONSE 

260 IF RESPONSE=l THEN GOSUB VALUES 
270 IF RESP0NSE=2 THEN GOSUB PLAY 
28 0 IF RESP0NSE=3 THEN GOSUB NUMBERS 
290 GOTO 240. REM REPEAT MAIN LOOP 
30 0 REM x 

310 REM x MENU 
320 REM x 
33 0 PRINT 

340 PRINT "WOULD YOU LIKE TO:" 

35 0 PRINT " 1. TYPE IN A TUNE," 

36 0 PRINT " 2. PLAY YOUR TUNE*" 
3^0 PRINT " 3, LIST THE NOTES*" 
^ PRINT 

390 PRINT "TYPE IN A NUMBER" J 
400 PRINT :rem INPUT IN MAIN LOOP 
410 RETURN 
50 0 REM x 

510 REM x INPUT VALUES FOR NOTES 

520 REM x 

530 PRINT " TYPE IN NUMBERS BETWEEN 0" 
540 PRINT " AND 255 TO BE THE NOTES" 

55 0 PRINT " OF A TUNE. TYPE ONE NOTE" 

56 0 PRINT " PER ?. WHEN YOU ARE FINISHED," 
570 PRINT " TYPE A -1 FOR THE LAST NOTE." 
5J>0 INPUT PITCH 

59 0 IF PITCH>255 OR PITCHOl THEN 580 

60 0 REM x MINUS ONE IS A FLAG FOR THE END OF THE DATA 
610 IF PITCH*- 1 THEN NUMNOTES=XNOTE ! RETURN 
620 XNOTE=XNOTE+l .REM NOTES COUNTER 
630 TUNE(XNOTE)=PITCH 
640 GOTO 580 
700 REM x 

710 REM x PLAY TUNE 

720 REM x 

730 FOR XNOTE=l TO NUMNOTES 
740 SOUND O, TUNE(XNOTE) , 10 , 10 
750 FOR DELAY=1 TO 10. NEXT DELAY 
. i3 NEXT XNOTE 
770 SOUND 0 t 0,0,0 
780 RETURN 
900 REM x 

910 REM x LIST NOTES 

920 REM x 

930 FOR XNOTE=l TO NUMNOTES Copyright Atari, Inc. 19S3. 

940 PRINT "TUNEC'JXNOTE;")";" ";TUNE(XNOTE) 11 

OCA MPVT VMHTC 



ARRAYS 

( Continued ) 



Activity 



Thus far we have used INPUT to fill the elements of an 
array* It is also possible to fill an array by READing DATA 
from within a program into an array* For example* music data 
could be stored in the program* read into an array* and 
sections of the array could be called at given tines in order 
to play a verse and then repeat a Melody* 

However* be careful with the READ statement* In Atari 
BASIC the READ instruction will only accept a simple 
variable* not an indexed variable* For example* the computer 
will accept the following READ statement* 

READ XNOTE 

The computer will not accept the following* 

READ TUNE ( 3 ) or READ TUNE ( XNOTE) 

Thus* you must READ the DATA into a simple variable and then 
transfer that value into the array* 



READ NUMBER ♦ TUNE(l) = NUMBER 

or 

READ NUMBER I TUNE ( XNOTE ) = NUMBER 



Have the campers RUN the TUNE program on their BASIC 
Utility Disk and look over the program in their^ program 
listings* The TUNE program is essentially the same as the 
MUSIC program in the READ* DATA* AND RESTORE Module* 
However ♦ having the data in an array enables you to repeat 
any note or sequence of notes in the tune* Have the campers 
experiment with changing the values for START and FINISH in 
order to make up different tunes* 



Copyright Atari* Inc* 1983* All rights reserved* 

12 



«£% FC Fc & Y S 

( Continued ) 



100 REM x TUNE ARRAY 

110 REM x 

120 DIM PITCHC50) ,DISTORT(50> ,LOUD<50> ,TIME<50) 
130 INIT=500:REM INITIALIZATION LINE* 

140 play=3oo:rem play tune routine 

150 MAXNOTES=ll 
20 0 REM x 

210 REM xxxxx MAIN LOOP xxxxx 

220 REM x 

230 GOSUB INIT 

240 start=i:finish=5:gosub PLAY 

25 0 START=6tFINISH=ll t GOSUB PLAY 
260 START=1 J FINISH=4 : GOSUB PLAY 
270 END 

300 REM 

^^0 REM xxxxx PLAY xxxxx 
REM x 

330 REM x PLAYS A SEQUENCE OF NOTES USING DATA ARRAYS. 
340 REM x INDICES DETERMINED BY VALUES OF START AND 
350 REM x FINISH IN MAIN LOOP 
360 REM x 

370 FOR XNOTE=START TO FINISH 

380 SOUND 0 » PITCH ( XNOTE) , DISTORT ( XNOTE ) , LOUD ( XNOTE ) 
370 FOR DELAY=1 TO TIME ( XNOTE K NEXT DELAY 
400 NEXT XNOTE 
410 RETURN 
420 REM x 

50 0 REM xxxxx INIT ARRAY xxxxx 
510 REM x 

520 FOR FILL=1 TO MAXNOTES 

530 READ PITCH, DISTORT, LOUD, TIME 

54 0 PITCH < FILL ) =PITCH : DISTORT ( FILL ) =DISTORT : LOUD ( FILL ) =LSUD : TIME < FILL ) =TIME 
550 NEXT FILL 
560 RETURN 

57 0 DATA 121,10,10,40,91,10,10,37,0,0,0,3,91,10,10,40,108,10,10,28 

58 0 DATA 0,0, 0,2, 108, 10, 10, 10, 91, 10, 10, 30, 108, 10, 10, 10, 121, 10, 10, 80, 0,0, 0,0 



Copyright Atari, Inc. 1983. All rights reserved. 

13 



ARRAYS 

(Continued) 



Activity *5 



A Group Discussion* 

In each of the programs where an array was used, all the 
data needed to be stored before you could do anything with 
it* For example* in the first program* you needed to know 
all the numbers before you could print then in the reverse 
order* In the SOUNDARY program* all the pitch values needed 
to be stored before they could be played back as a tune* 
Arrays are especially useful whenever you need to have access 
to all of the data before any thing is done with it* Ask the 
campers to think about each of the following programing 
problems and explain why using an array is or is not a good 
idea in each case* 



Find the average of five numbers that are INPUT by the 
program user* (Answer* No* because the numbers can be added 
together as they are INPUT into the computer and then divided 
by the number of values typed in*) 



SUM = 0 

FOR COUNT = 1 TO 5 
INPUT NUM 
SUM = SUM + NUM 
NEXT COUNT 
AVERAGE ■ SUM/5 



Given a list of numbers ♦ which numbers are larger than 
the average of the numbers* (Answer J Yes* All the numbers 
must be saved in order to look back and see which are greater 
than the average*) Ask campers to try to solve this without 
an array* What if you knew there would only be five numbers? 



Can you think of some more examples? 



Copyright Atari* Ir.c* 1983* All rights reserved* 

14 



F" R: O G R A M M X M & CHALLENGES USXNG 

ARRAYS 



1* Store your own tune data in the SOUNDARY progran* READ 
it into an array and play different sequences of notes from 
the nain loop* 



2* Give the person using your program the option to edit his 
or her tune, one note at a tine* Ask the person which note 
he or she wants to change and use that number as the index to 
your array* Then ask what the new note value will be* 
Change the array element accordingly and return to the menu* 



3* Write a program which INPUTs a series of numbers* and 
then lists those numbers which are larger than the average of 
all the numbers which were typed in* Use an array to store 
the values which the person types in* 

4* Use two different arrays* HUE(IOO) and LUh(lOO)* to 
create a light show* Your program should contain a statement 
like the following onet 

SETCOLOR 0*HUE(COUNT) *LUM(COUNT) 



Copyright Atari* Inc* 1983* All rights reserved* 

15 



ARRAYS 

CAMPER COPY 



10 0 REM x ARRAY OF NUMBERS 

110 REM x 

120 MAXNUMS = 5 {REM MAXIMUM NUMBERS WHICH CAN BE INPUT 
130 DIM NUMS(MAXNUMS) 
140 REM x 

150 REM * FILL ARRAY 

160 REM * 

170 FOR COUNT = 1 TO MAXNUMS 
180 PRINT "TYPE IN A NUMBER"; 
190 INPUT VALUE 

200 NUMS(COUNT) - VALUE {REM STORE INPUT VALUE IN ARRAY 
210 NEXT COUNT 



220 REM * 

230 REM x PRINT NUMBERS IN ORDER 

240 REM x 
250 PRINT 

260 PRINT "YOU TYPED IN THE NUMBERS IN THE" 
270 PRINT "FOLLOWING ORDER ♦ " 
280 PRINT 

290 FOR COUNT = 1 TO MAXNUMS 

30 0 PRINT NUMS ( COUNT ) }" "{ {REM PRINT VALUE + SPACES 
310 NEXT COUNT 
320 PRINT 



100 REM * SOUND WITH AN ARRAY 

110 REM x 

120 DIM TUNE(IOO) 

130 XNOTE = 0 

140 INPUT PITCH 

150 IF PITCH = -1 THEN NUMNOTES = XNOTE{GOTO 200 

160 XNOTE = XNOTE + 1 

170 TUNE < XNOTE ) ■ PITCH 

180 GOTO 140 



Copyright Atari, 



Inc. 1983. All rights reserved. 
16 



Ft Fi Y S 

CAMPER COPY CONTINUED 



200 REM x 

210 REM x PLAY TUNE 

220 REM x 

230 FOR XNOTE = 1 to NUMNOTES 

240 SOUND 0 , TUNE ( XNOTE ) , 1 0 , 1 0 

250 FOR DELAY = 1 TO 1 0 ♦ NEXT DELAY 

260 NEXT XNOTE 

270 SOUND 0,0,0,0 



100 REM x SOUND WITH AN ARRAY PLUS PLAY TUNE 

110 REM x 

120 .DIM TUNE(IOO) 

130 XNOTE = 0 

140 INPUT PITCH 

150 IF PITCH « -1 THEN NUMNOTES = XNOTEJGOTO 200 
160 XNOTE = XNOTE + 1 
170 TUNE (XNOTE ) = PITCH 
180 GOTO 140 
20 0 REM x 

210 REM x PLAY TUNE 

220 REM x 

230 FOR XNOTE = 1 to NUMNOTES 

240 SOUND 0 ,TUNE(XNOTE) ,10,10 

250 FOR DELAY = 1 TO 10J NEXT DELAY 

260 NEXT XNOTE 

270 SOUND 0,0,0,0 



Copyright Atari, Inc. 1983* All rights reserved* 

17 



ARRAYS 

CAMPER COPY CONTINUED 




100 REM x SOUND ARRAY 

110 REM x 

120 REM x SOUNDARY 

130 REM x INITIALIZE VARIABLES AND ARRAY 

14.0 REM x 

150 DIM TUNE(IOO) 

160 XNOTE=0 

165 REM x ASSIGN LABELS TO LINE NUMBERS 

170 MENU=300 

180 VALUES=50O 

190 PLAY=700 

ZOO NUMBERS=90 0 

210 REM x 

220 REM x MAIN LOOP 

230 REM x 

240 GOSUB MENU 

250 INPUT RESPONSE 

260 IF RESPONSES THEN GOSUB VALUES 
270 IF RESP0NSE=2 THEN GOSUB PLAY 
280 IF RESP0NSE=3 THEN GOSUB NUMBERS 
0 GOTO 24 0: REM REPEAT MAIN LOOP 
0 REM x 
310 REM x MENU 
320 REM x 
330 PRINT 

34 0 PRINT "WOULD YOU LIKE TOt" 
350 PRINT " 1. TYPE IN A TUNE." 

360 PRINT " 2. PLAY YOUR TUNE." 

370 PRINT " 3. LIST THE NOTES." 

380 PRINT 

390 PRINT "TYPE IN A NUMBER" * 
100 PRINT :REM INPUT IN MAIN LOOP 
410 RETURN 
500 REM x 

510 REM x INPUT VALUES FOR NOTES 

520 REM x 

530 PRINT " TYPE IN NUMBERS BETWEEN 0" 

54 0 PRINT " AND 255 TO BE THE NOTES" 

550 PRINT " OF A TUNE. TYPE ONE NOTE" 

560 PRINT " PER ?. WHEN YOU ARE FINISHED," 

57C PRINT " TYPE A -1 FOR THE . LAST NOTE." 

SCO INPUT PITCH 

59 0 IF PITCH>255 OR PITCHOl THEN 580 

£0 0 REM x MINUS ONE IS A FLAG FOR THE END OF THE DATA 
610 IF PITCH=-1 THEN NUMNOTES=XNOTE : RETURN 
S20 XNOTE=XNOTE+i:REM NOTES COUNTER 
0 TUNE(XNOTE)=PITCH 
GOTO 580 




Copyright Atari, Inc. 1983. All rights reserved. 

18 



ARRAYS 

CAMPER COPY CONTINUED 



TUNE 



REM X 



TUNE ARRAY 



110 REM x 

120 DIM PITCH<50> ,DISTORT<50> ,LOUD<50> ,TIME<50> 

130 init=soo:rem INITIALIZATION LINE* 
140 PLAY=300:REM play tune routine 

150 MAXNOTES=ll 
200 REM x 

210 REM xxxkx MAIN LOOP xxxxx 

220 REM x 

230 GOSUB INIT 

240 START=1 * FINISH=5 J GOSUB PLAY 

250 start=6:finish=ii :gosub PLAY 
260 start=i:finish=4:gosub play 

270 END 
300 REM 



32TT REM x . 

330 REM x PLAYS A SEQUENCE OF NOTES USING DATA ARRAYS. 
34 0 REM x INDICES DETERMINED BY VALUES OF START AND 
350 REM x FINISH IN MAIN LOOP 
360 REM x 

370 FOR XNOTE=START TO FINISH 

380 SOUND 0 , PITCH ( XNOTE ) , DISTORT ( XNOTE ) , LOUD < XNOTE ) 
390 FOR DELAY=1 TO TIME < XNOTE) : NEXT DELAY 
40 0 NEXT XNOTE 
410 RETURN 
420 REM x 

50 0 REM xxxxx INIT ARRAY xxxxx 
510 REM x 

520 FOR FILL=1 TO MAXNOTES 
530 READ PITCH, DISTORT, LOUD, TIME 

54 0 PITCH ( FILL )=PITCH: DISTORT < FILL )=DISTORT: LOUD ( FILL )=LflUD: TIME ( FILL )=TIME 
550 NEXT FILL 
560 RETURN 

57 0 DATA 121, 10, 10, 40, 91, 10, 10, 37, 0,0, 0,3, 91 , 10, 10, 40, 108, 10, 10, 28 

58 0 DATA 0,0,0,2,108,10,10,10,91,10,10,30,108,10,10,10,121,10,10,80,0,0,0,0 




REM xxxxx PLAY xxxxx 




Copyright Atari, Inc. 1983. All rights reserved. 

20 



MATRICES 



An even more complex and more powerful array is called a 
"Matrix" or a "two dimensional array*" A matrix is an array 
of arrays* which is best explained with diagrams* The 
activities in this module take the campers through the steps 
required to write a battleship game that uses a matrix* 

If you would like to read about two dimensional arrays, 
or review some applications for matrices, you may want to 
look through the following references* (These are the same 
resources that were listed in the Arrays Module*) 



ATARI ^00/800 BASIC Reference Manual: pp*3* ^1-^3 
Inside Your Atari* pp* 66-7^ 
Your ATARI Computer t pp* 65-67 



Suppose you had a list of swimmers 7 times from three 
different swim meets* And* suppose you wanted to compare 
each swimmer's time for the butterfly in each of the three 
meets* A matrix is especially well-suited to Just such a 
problem* The following diagram illustrates how the swimmers' 
data can be stored in a matrix* 



SWIM MEETS 



SWIMMER #1 



SWIMMER #2 



SWIMMER *3 



SWIMMER M 



25 



31 



28 



37 



8 



30 



^2 



8 



35 




TIMES 



The swim times for each meet are stored in separate 
columns* The swimmers are listed in the rows of the matrix* 
Swimmer number one swam the race in the second meet in 28 
seconds* In BASIC* this is written in the following way* 



Copyright Atari* Inc ♦ 



1983* 
1 



All rights reserved* 



MATRICES 

( Continued ) 



SWIMMER < 1 #2) = 28 
/ \ 
ROW COLUMN 
SWIMMER* MEET* 



Two indices are used* One holds the row value, which is 
the SWIMMER number* The second index is the colunn value, 
which in this case is the swim meet nunber* Swinner nunber 
three's slowest tine was in the second Meet* 



SWIMMER<3*2) ■ 30 
/ \ 
ROW COLUMN 
SWIMMER* MEET* 



Activity *1 



1* Any data which conveniently fits into a grid or Matrix 
format* is well-suited to a two dimensional array in a BASIC 
program* Describe some programming examples in which you 
might use a two dimensional array* Explain the format of the 
indices for accessing an element of the matrix* Draw a 
matrix similar to the SWIMMER matrix on the board* Give the 
campers an opportunity to practice with indices by presenting 
some sample statements to complete* like the following 
examples* 

SWIMMER(3*1) = 

SWIMMER(2,1) = 4 

SWIMMER(3*_) = 26 
SWIMMER<_, 1 ) = 28 



2* The format of a DIM statement for a matrix is shown 
below* 



DIM SWIMMERS, 3.) 

/ \ 

Maximum * Maximum * 
of rows* of columns 

\ / 

In the matrix called 
SWIMMER* 



Copyright Atari* Inc* 1983* All rights reserved* 



Activity *2 



1* The next prograhMing activity involves developing 3 BASIC 
progran for 3 "battleship" qawe* It May be helpful for the 
canpers to be 3ble to sinulate the progran on the board 
first* Draw 3 four by four Matrix on the boards like the one 
below ♦ 



COLUMNS 

12 3 4 
1 X LOCATION < 1 ,2) 

R 

0 2 
W 

S3 
4 



In the prograMt the randoM number function will be used 
to secretly position 3 host on the hoard* For now* play the 
gane on the blackboard* Ask one canper to secretly decide 
where the boat will be hidden on the battleship gane board* 
Then have the other canpers guess where the boat is by giving 
the matrix nane and the indices of the guessed location* 
List the guesses on the board beside the Matrix and place an 
"X" on the Matrix for each incorrect guess* Do this until 
the boat is found* You M3y want to play the gaine a couple of 
tines in order to give the canpers practice with using two 
indices ♦ 



Copyright Atari* Inc* 1983* All rights reserved* 

3 



( Continued ) 



Activity *3 



1 * To program this probleM^ first we Must be sure that the 
battleship board is cleared to zero, so that no extraneous 
data in Menory interferes with the game* This is called 
initializing the array* Explain that variables can be used 
as indices to a matrix* For example, BOARD < ROW * COLUMN ) = 0 * 
will place a zero in the specified location in the matrix* 
Ask the campers to suggest how they might initialize the 
BOARD matrix, using two nested FOR loops (like the example 
listed in number 2 below)* Record the initialization routine 
on the board* as the campers plan it* Draw a ^X^ matrix on 
the board* like the one above* and step through the loop 
routine, placing zeros in the matrix everytime a zero is 
assigned to a location* 



2 ♦ Have the campers compare their code with the 
initialization routine listed below* Ask the campers to type 
in the following subroutine* Note that a variable can be 
used to dimension the matrix* 



130 REM x 

140 MAXL0CATI0NS=4 

150 DIM BOARD (MAXLOCATIONS*MAXLOCATIONS) 

160 COLUMN=0 :ROW=0 

200 REM * 

210 REM * I NIT MATRIX 

220 REM x * 

230 FOR ROW * 1 TO MAXLOCATIONS 

240 FOR COLUMN = 1 TO MAXLOCATIONS 

250 B 0 A R D < ROW f COLUMN > * 0 ♦ R E M STORE A 0 

260 PRINT LOCATION<ROW*COLUMN> 

270 NEXT COLUMN 

2S0 NEXT ROW 



Line 260 prints the contents of each element of the 
matrix* RUN the program to confirm that each element of the 
matrix got a zero as planned* E'.e sure the campers understand 
how the nested FOR loops work in lines 230 and 2^0 by 
"playing computer" and filling in a matrix on the blackboard 
in the order the computer does it* 



100 
110 
120 



REM * 
REM x 
REM x 



BATTLESHIP 



INITIALIZE VARIABLES 



Copyright Atari, I no 1983* All rights reserved* 



( Cont i nued ) 



3* Now the ship nust be hidden* Two randoh numbers Must be 
generated, one for the row value and one for the colu«n value 
in order to hide a ship in the matrix* A one is placed in 
the natrix in the location of the hidden ship in order to 
distinquish it from the empty spaces (zeros) on the board* 
Go over the following routine with the campers* Explain why 
and how the random numbers were used for the ship's location* 
Discuss why a one is put in the location of the ship* Ask 
campers what they think BOARD < SHIPROW , SHIPCQL > = 1 will do* 
Have the campers add the following code to their program 
which initializes the battleship matrix* 



^00 REM * 

410 REM X PLACE SHIP 

420 REM x 

430 SHIPROW ■ INT (RND ( 0 ) *40* 1 t REM A RANDOM NUMBER 

440 SHIPCQL " INT ( RND ( 0 > +4 ) + 1 *REM BETWEEN 1 AND 4 

450 BOARD (SHIPROW f SHIPCOL ) * 1 *REM ONE IS ASSIGNED TO RANDOM LOCATION 



4* To play the game you must INPUT the user's guess and see 
if there is a "one" stored in that location* If the contents 
of the guessed location is one* the ship has been found* If 
not* let the user guess again* Explain* in English* the 
sequence of steps the program must take in order for someone 
to play the game* Have the campers come up with the BASIC 
code* Record the campers suggestions on the boardt as they 
are given* 

1* First* get the user's INPUT for the ROW value* 

print u row; ";: input rowguess 



Get the COLUMN value* 
PRINT ''COLUMN: " J ♦ INPUT COLGUESS 



3* Check to see if the location in the matrix guessed 
by the program user holds a ship* If so* PRINT "YOU FOUND 
IT!"* 

IF BOARD < ROWGUESS , COLGUESS ) « 1 THEN PRINT "YOU FOUND IT!"*END 



Copyright Atari* Inc* 1983* All rights reserved* 



MATRICES 

( Continued ) 



4, Otherwise PRINT "TRY AGAIN" and go back to the line which 
INPUTS the ROW value. 



Conpare the canpers' listing with the gane play routine 
below ♦ 



700 
720 
730 
7^0 
750 
760 
770 
780 
790 
800 
810 
820 
83 0 
840 



1 1 



TYPE IN THE COORDINATES OF" 
"YOUR GUESS » THE NUMBER MUST " 
BE BETWEEN 1 AND 



1 1 



REM * PLAY 
REM x 
PRINT 
PRINT 
PRINT 
PRINT 

PRINT "row: 

INPUT ROWGUESS 
PRINT "COLUMN: 
INPUT COLGUESS 

IF BOARD (ROWGUESS, COLGUESS )=1 THEN PRINT 
PRINT 

PRINT "TRY AGAIN" 
GOTO 770 



1 1 ♦ 



ll ♦ 
f 



"YOU F r OUND IT ! » t END 



Have the csnpers type in the PLAY routine* Renefiber ♦ 
the Matrix is only a ^X*t Matrix* Rewind campers that if they 
type in a coordinate for the ship which is less than one or 
greater than four the program will bonb* 



Act i vity 4-4 



1« To see how the sane code can be dressed up with a few 
PRINT statements, RUN the SHIP program on the BASIC Utility 
Disk* 



Copyright Atari* Inc* 1983* All rights reserved* 

6 



PROGRAMMING CHALLENGES USIENG 

MATRICES 



1* Place nore than one ship on the battleship board in 3 
randon location for the user to find* 



2* Make the ship larger ♦ so that it takes up two or three 
locations on the grid of elements in the Matrix* Give the 
outer limits of the ship different values than the middle of 
the ship* This way* you can give the player feedback on his 
or her guess* (eg* "You hit the front of the ship*") 



3* Give the player hints in response to his or her guesses* 
For example* if the program player's guess for the row 
position is one away froM the ship, PRINT "YOUR ROW GUESS IS 
HOT!" If the next row guess is nore than one away from the 
ship's location* PRINT "YOUR ROW INDEX IS GETTING COLDER ♦ " 
Do the sane for the column values* 



^* Place friendly ships and enemy ships on the game board* 
Give the friendly ships one value and the enemy ships another 
value in order to differentiate the two* Keep score for the 
player* When an enemy ship is encounter ed * the player gains 
points* When an allies ship is hit* the player looses 
points * 



5* Experiment with different graphics nodes* drawing a grid* 
and displaying the actual ships on the screen* 



Copyright Atari* Inc* 1983* All rights reserved* 

7 



MATRICES 

Csnper Copy 



xxxxx BATTLESHIP xxx*x 



100 REM * BATTLESHIP 

110 REM X 

120 REM * INITIALIZE VARIABLES 

130 REM * 

140 MAXL0CATIGNS=4 

150 DIM BOARD < MAXLOC ATIQNS f MAXLOCATIONS ) 

160 COLUMN=0 :ROW=0 

200 REM x 

210 REM * INIT MATRIX 

220 REM x 

230 FOR ROW = 1 TO MAXLOCATIONS 

240 FOR COLUMN = 1 TO MAXLOCATIONS 

250 BOARD(ROW,COLUMN>=0 

260 PRINT LOCATION(ROW, COLUMN) 

270 NEXT COLUMN 

280 NEXT ROW 



xxxxx PLACE SHIP xxxxx 



400 REM x 

410 REM * PLACE SHIP 

420 REM * 

430 SHIPROW = INT(RND< 0 )*40+l ! REM A RANDOM NUMBER 

440 SHIPCOL * INT ( RND < Q ) +4 ) + 1 5 REM BETWEEN 1 AND 4 

450 BOARD<SHIPRQW,SHIPCQL)=l :REM ONE IS ASSIGNED TO RANDOM LOCATION 



Copyright Atari, Inc. 1983* All rights reserved* 

8 



Cshper Copy Continued 



xxxxx PLAY xxxxx 



70 0 REM * PLAY 

720 REM * 

730 PRINT "TYPE IN THE COORDINATES OF" 

740 PRINT "YOUR GUESS ♦ THE NUMBER MUST" 

750 PRINT "BE BETWEEN 1 AND 

760 PRINT 

770 PRINT "ROW t "J 

780 INPUT ROWGUESS 

790 PRINT "COLUMN: " \ 

80 0 INPUT COLGUESS 

810 IF BOARD(ROWGUESStCOLGUESS)=l THEN PRINT "YOU FOUND IT!":END 

820 PRINT 

830 PRINT "TRY AGAIN" 

840 GOTO 770 



Copyright Atari, Inc* 1983* All rights reserved* 

9 



MATRICES 

Canper Copy Continued 



10 0 REM * BATTLE SHIP 

110 REM x 
120 REM x 

130 REM x INITIALIZE VARIABLES 
140 REM * 

150 MAXL0CATI0NS=4 

160 DIM BOARD ( MAXLOCATIONS* MAXLOCATIONS ) 
170 COLUMN=0 :ROW=0 

175 REM ASSIGN NAMES TO SUBROUTINE LINE NUMBERS 

180 INITMATRIX=500 

19 0 PLACESHIF-7 0 0 

200 PLAY=900 

210 WIN=1300 

300 REM x 

310 REM x MAIN LOOP 

320 REM x 

330 GOSUB INITMATRIX 
340 GOSUB PLACESHIP 
350 GOSUB PLAY 
360 END 
50 0 REM x 

510 REM x INIT MATRIX 

52 0 REM x 

530 FOR ROW*l TO MAXLOCATIONS 
540 F r O R COLUMNS TO MAXLOCATIONS 
550 BOARD (ROW, COLUMN >=0 
560 PRINT BOARD (ROW, COLUMN) 
570 NEXT COLUMN 
58 0 NEXT ROW 
590 RETURN 
70 0 REM x 

710 REM x PLACE SHIP 

720 REM x «? 

730 SHIPR0W=INT<RND(Q>*4)+1 :REM RANDOM NUMBER 
74 0 SHIPCOL«INT < RNDC Q ) *4 > + 1 J REM BETWEEN 1 AND 4 

750 BOARD ( SHIPROW, SHIPCOL > =1 : REM PLACE SHIP IN RANDOM LOCATION 

760 RETURN 

90 0 REM x 

910 REM x PLAY 

920 REM x 

930 GRAPHICS 2 

940 POSITION 0,0 

95 0 PRINT #6 J 1 ' columns" 

960 FOR NUMBER*! TO 4 

970 POSITION 2,NUMBERx2tREM ROW COORDINATES 

980 PRINT #6? NUMBER 

990 POSITION NUMBERx4,l :REM COLUMN COORDINATES 
1 0 0 0 PRINT 4-6 t NUMBER 
1010 NEXT NUMBER 



Copyrioht Atari, Inc* 1983* All rights reserved* 

10 



MATRICES 

Csnper Copy Continued 



1020 
10 3 0 
1 0 4 Q 
1050 
10 6 0 
107 0 
1080 
10 9 0 

110 0 

1 1 1 0 
1120 
1130 
11*0 

115 0 

1 16 0 

117 0 
11 30 

1190 
1300 
1310 

132 0 

133 0 
1340 
1350 

136 0 

137 0 

138 0 

1 39 0 

140 0 
1410 
1420 



0,3 {PRINT *61 ,I R* 
0,4 J PRINT ♦Ai'VO" 
0*5* PRINT *6;"W" 

o, 6: print #6; i, s n 
type in the coordinates 
your guess » the number 
be between 1 and 4 
••row: 



POSITION 
POSITION 
POSITION 
POSITION 
PRINT 
PRINT 
PRINT 
PRINT 
INPUT ROWGUESS 
IF ROWGUESS<i OR 
PRINT "COLUMN 
INPUT COLGUESS 
IF C0LGUESS<1 OR 



1 1 



1 1 



1 1 



OF" 
MUST " 



1 1 



1 1 ♦ 



R0WGUESS>4 THEN 1090 



it ♦ 

t 



THEN 1120 



C0LGUESS>4 

IF BOARD (ROWGUESS, COLGUESS )=1 THEN GOSUB WIN J RETURN 
POSITION C0LGUESSx4rR0WGUESSx2rREM PUT x ON BOARD 
PRINT *6r ,, * H 



PRINT : PRINT "TRY 
GOTO 1090 
REM * 

REM * WIN 
REM x 
PRINT 



AGAIN" 



FOUND IT ! " 



♦PRINT "YOU 
FOR CQUNT=1 TO 10 
POSITION C0LGUESS*4 t ROWGUESSX2 
PRINT #6;" " J ♦REM ERASE X 
FOR DELA Y~ 1 TO 75 t NEXT DELAY 
POSITION C0LGUESSX4 , R0WGUESS*2 

print *6; m *";:rem flash x 

FOR DELAY-1 TO 75tNEXT DELAY 

NEXT COUNT 

RETURN 



Copyr iqht 



Alar i , Inc * 



1933* 
11 



All rights reserved* 



PEEK & ND F> O K EH 



In the sane way that human beings have all sorts of 
pieces of information stored in their brain like telephone 
numbers and lock combinations* the computer also maintains 
hundreds of pieces of information ♦ When you turn on your 
computer the operating system stores all the necessary 
information the computer needs to process your programs* The 
PEEK instruction enables you to look at the contents of any 
memory location. The POKE instruction allows you to change a 
value stored in memory* 



To read more about the PEEK and POKE instructions* you 
may want to consult the following books* 



Atari 400/800 BASIC Reference Manual: pp* 35 

Inside Atari BASIC ♦ pp 132-13? 

Your Atari Computer: pp 113* 379* 398 



All the information stored in memory is stored in the 
form of numbers* Each number is held in a separate location* 
Memory can be thought of as a long series of boxes* each 
holding one piece of information* a number* There are 65*536 
memory locations in a 64K Atari* Each box or memory location 
has an address which enables the programmer to identify which 
of the memory locations he or she is referring to* When you 
use the PEEK or POKE instructions you must specify the 
address of the memory location you want* 



The PEEK instruction enables us to peer in at the 
contents of the specified memory location* For example* 
PEEK(82) is the value stored in memory location 82* The 
address of the memory box you want to look at in this 
example, 82* is listed in parentheses following the PEEK 
instruction* Memory location 82 happens to hold the number 
of spaces used by the computer to set the left margin on the 
screen* To see the number of spaces that the left margin is 
currently set to* type the following instruction* 



PRINT PEEK (82) 



Have you ever noticed that there are two blank spaces on 
the left hand side of the screen* This is because the left 
margin* memory location 82* is set to 2 by the operating 
system* when you turn on your computer* 



Copyright Atari* Inc* 1983* All rights reserved* 

1 



PEEK **MD POKE 

(Continued) 



The POKE instruction enables you to change a value 
stored in Menory* For example* we could use a POKE 
instruction to change the left Margin ♦ 



POKE 82,5 



To poke a value into Menory> the address of MeMory is 
listed, followed by a comm3 and the new value to be stored in 
«e*ory* Have the canpers type in the POKE 82,5 instruction 
to see what happens* Experiment with poking the following 
values into «enory for the left Margin* Retype the entir 
instruction using the values listed below* 



5, 10, 20, 39 



After poking 3? into nenory location 82, have the 
canpers try to Move the cursor to the left or to the right* 
Ask the canpers why the cursor will not Move to the left or 
right* 

It is also possible to use a variable as the value to be 
poked into MeMory with the POKE instruction* For exaMple, if 
COUNT is 1 then POKE 82, COUNT will store a 1 in MeMory 
location 82* Have the campers type in the following routine 
that uses a variable in a FOR * * NEXT loop to change the 
setting of the left Margin* 



10 REM ** POKING THE LEFT MARGIN 

20 REM * 

30 PRINT 

40 FOR LEFTMARGIN - 0 "TO 39 STEP 5 

50 POKE 82, COUNT 

60 PRINT 

70 PRINT "LEFT MARGIN " 

80 NEXT LEFTMARGIN 



RUN the prograM# Then ask the canpers to LIST their 
prograM* Why does everyone's code look so peculiar? 
Encourage the canpers to experinent with changing the values 
in this routine and running the prograM* 



Copyright Atari, Inc* 1983* All rights reserved* 

2 



PEEK tf=*MD POKE 

(Continued) 



The value for the right margin is stored in memory 
location 83* Have the campers type the following instruction 
to see what the right margin has been set to* 

* 



PRINT PEEK<83) 



The right Margin is routinely set to 39 * the last column 
on the graphics zero screen* Try poking a 20 into memory 
location 83* 

POKE 83,20 



Have the campers try all sorts of values* If they get 
to a point where they are unable to return the margin to a 
reasonable setting* press SYSTEM RESET to reset the margins 
to their customary setting* Have the campers type in the 
following routine and RUN it* The program is simply a loop 
which continuously decrements the right margin by 5* 



100 REM *xx*x DECREMENT RIGHT MARGIN 

110 REM x 

120 PRINT 

130 FOR RIGHTMARGIN m 39 TO 0 STEP -1 

140 POKE 83 ♦ RIGHTMARGIN 

150 PRINT "RIGHT MARGIN" i 

140 FOR DELAY - 1 TO 50* NEXT DELAY 

170 NEXT RIGHTMARGIN 



Once again* when the program is completed the margins 
are so close together that the computer does not understand 
any instructions which are typed im Press SYSTEM RESET to 
return the margins to normal* Then have the camper LIST the 
routine* Typing SYSTEM RESET does not affect the program in 
memory* 



Now have the campers type in the following POKE 
instruction* 



POKE 755*6 



Copyright Atari* Inc* 1983* All rights reserved* 

3 



F > E E K AND POK IE 

(Continued) 



All the letters on the screen should be inverted* To 
return the letters to their upright position type the 
following POKE instruction* 

. ■ . 
POKE 755,2 

For wore locations to PEEK ♦ POKE* and play with* see the 
following resources* 

Atari Connection* Sunner ♦ 1983* pp 31-32 
Inside Atari BASIC: pp 132-139 
Master MeMory Map 



All of these references are available in the caMP 
library* 



The sunner issue of The Atari Connection has an article 
entitled "PEEKS AND POKES* CoMMonly Used and Helpful Mewory 
Locations*" This article has lots of fun ideas for 
exper inenting with PEEK and POKE and an explanation for each 
exanple* 



Inside Atari BASIC also suggests various locations to 
PEEK and POKE for fun* 



The Master Menory Map* produced by Educational Software 
Inc** lists all the significant newory locations* their 
contents* and what changes you can Make* Encourage the 
caMpers to look over the MeMory Map and experinent with 
changing the suggested locations* And finally* reassure the 
caMpers that it is iMpossible to danage or perManently alter 
MeMory* Have fun! 



Copyright Atari* Inc* 1983* All rights reserved. 

4 



PEEK AMD POKEI 

CAMPER COPY 



xxxxx PEEK AT THE LEFT MARGIN SETTING xxxxx 



PRINT PEEK (82) 



xxxxx POKE THE LEFT MARGIN WITH A NEW VALUE xxxxx 



5, 10, 20, 39 



xxxxx POKING THE LEFT MARGIN USING A VARIABLE xxxxx 



10 REM xx POKING THE LEFT MARGIN 
20 REM * 
30 PRINT 

40 FOR LEFTMARGIN m 0 TO 3? STEP 5 
50 POKE 82, COUNT 
60 PRINT 

70 PRINT "LEFT MARGIN " 
80 NEXT LEFTMARGIN 



xxxxx PEEK AT THE RIGHT MARGIN xxxxx 



PRINT PEEK (83) 



xxxxx POKE THE RIGHT MARGIN xxxxx 



POKE 83,20 



Copyright Atari, Inc, 1983. All rights reserved 



F > EEL EE l-C 
CAMPER 



AND F-OKE 
COPY CONTINUED 



xxxxx POKING THE RIGHT MARGIN WITH A VARIABLE xxxxx 



100 REM xx DECREMENT RIGHT MARGIN 

110 REM x 

120 PRINT 

130 FOR RIGHTMARGIN - 39 TO 0 STEP -1 

H0 POKE 83 f RIGHTMARGIN 

150 PRINT "RIGHT MARGIN" i 

160 FOR DELAY ■ 1 TO 50 J NEXT DELAY 

170 NEXT RIGHTMARGIN 



xxxxx INVERTED PRINT xxxxx 
POKE 755,6 

POKE 755,2 



xxxxx REFERENCES WITH MORE IDEAS FOR MEMORY LOCATIONS 

TO PEEK AND POKE xxxxx 



Atari Connection, SuMner,1983J pp 31-32 
Inside Atari BASIC! pp 132-139 
Master Mewory Map 



Copyright Atari, Inc* 



1983. 
6 



All rights reserved.