ARRAYS›                ======››             by Ron Fetzer››      There are 3 kinds of arrays that› we use in TURBO-BASIC or ATARI BASIC:›      1)One dimensional number array›      2)Two dimensional  number  array›        or MATRIX›      3)String Arrays(Pseudo-String›        Array)››       Arrays    are    also    called› Subscripted  Variables. P(2) = "P sub› 2". The P is the variable and  the  2› is  the  subscript.  The subscript is› always   in  parenthesis  P(3),  P(4)› etc.››       Arrays   are   very  useful  in› manipulating numbers and strings.  It› is  the ONLY way you can sort numbers› or alphabetize strings. You also save› on  variable  names,  you  can   save› numbers  or  words  in a program, you› can handle large amounts  of  numbers› or  strings and you can speed up your› program   execution.   This   is    a› very useful   technique    and     is› frequently used in many programs.››        ONE DIMENSIONAL ARRAYS›        ----------------------››      You   can   think   of   a   ONE› DIMENSIONAL  ARRAY  as  a  string  of› pearls.  Each  pearl is an element of› the array.››            PEARL NECKLACE››   -O----O----O----O----O----O----O-›› Element #›    0    1    2    3    4    5    6› Value $›  $25  $33  $42  $50  $38  $28  $22›››      In number arrays the 1st element› is 0. In the example above we have 7 › elments from 0 to 6. When we  use  an› array  we  must  DIM it. The DIM also› starts   with   0,   in   effect   we› dimensioned  for 7 elements or pearls› if we use DIM P(6). The  form  of  an› array is:››               P(X) = V›› P = The name of the array. You must›     DIM it for the number of›     elements you are going to have›     in your array.›› X = The element numbers. Usually›     a FOR - NEXT LOOP›› V = Inputs the value into each›     element as the loop executes››       ELEMENTS AND THEIR VALUE›› P(0)=25, P(1)=33, P(2)=42, P(3)=50,› P(4)=38, P(5)=28, P(6)=22››      Please  key  in  the  short demo› program to see how it works››      10 CLS:?:?›      20 DIM P(6)›      30 FOR X = 0 TO 6›      40 INPUT "THE VALUE OF EACH"›         PEARL";V›      50 P(X)=V:REM <-- ARRAY›      60 NEXT X›      70 PAUSE 60›      80 ? "LETS SEE IF IT WORKED"›      90 ?:INPUT "WHAT PEARL DO YOU›         WANT TO SEE(0-6)";S›      100 ? P(S):REM <-- ARRAY›      110 GOTO 90››      You now can call up any pearl or› element in the array and see its› value.››      You  also  can print out all the› values  of  the  pearls  or  elements› automatically. Change lines 90 to 110› as follows:››      90 ?: FOR Y = 0 TO 6›      100 ? "PEARL #";Y;" = ";P(Y):›         REM P(Y) IS THE ARRAY›      110 NEXT Y›››     2 DIMENSIONAL ARRAY OR MATRIX›     -----------------------------››      2  Dimensional  arrays or Double› Subscripted Variables are also called› a  MATRIX.  A  matrix is a grid where› you have columns and rows.›      For example lets take a  bowling› team  of 3 members and each one plays› 4   games.   This   is  how  you  can› visualize the matrix:››                BOWLERS››           1          2          3  ›          ----       ----       ----›   B(0,0)|250|B(0,1)|220|B(0,2)|240|› G        ----       ----       ----›          ----       ----       ----› A B(1,0)|210|B(1,1)|190|B(1,2)|250|›          ----       ----       ----› M        ----       ----       ----›   B(2,0)|240|B(2,1)|230|B(2.2)|270|› E        ----       ----       ----›          ----       ----       ----› S B(3,0)|220|B(3,1)|200|B(3,2)|260|›          ----       ----       ----›      In a matrix  the  first  element› also  starts  with  0. In the example› above we have a matrix  and  we  must› DIM  it DIM(2,3). The 2 in the DIM is› the 3 bowlers (0 to 2). The 3 in  the› DIM  is the 4 games (0 to 3). We have› a total of 3 x 4 or  12  elements  in› this 2 dimensional array.››      The  bowling  score  for  the  4› games were as follows:››      BOWLER 1  BOWLER 2  BOWLER 3›      --------  --------  --------››      250       220       240›      210       190       250›      240       230       270›      220       200       260››      In  the matrix the first element› is (0,0). We normally do not consider› 0  a number but the computer does not› make that distinction.››      Please key in  this  short  demo› program to see how it works››      10 CLS:?:?›      20 DIM B(2,3)›      30 FOR X=0 TO 2›      40 FOR Y=0 TO 3›      50 ? "BOWLER ";X+1;" GAME #";›         Y+1›      60 INPUT "SCORE PLEASE ";S›      70 B(X,Y)=S:REM <--MATRIX›      80 ?›      90 NEXT Y›      100 NEXT X›      110 ?:PAUSE 60›      120 ? "LETS SEE IF IT WORKED"›      130 INPUT "WHAT BOWLER(1-3)";P›      140 INPUT "WHAT GAME(1-4)";G›      150 ? "    ";B(P-1,G-1):REM›          MATRIX›      160 GOTO 130››      We  use nested loops to load the› matrix.  The  first  element  to  get› loaded is B(0,0). In line 50  we  use› X+1 for the bowler - if the loop is 0› then the bowler becomes 0+1 or 1.  We› did  the same thing for the games Y+1› so when the loop  furnishes  a  0  is› becomes  0+1  or  1.  We did the same› thing in line 150 except  in  reverse› so  the  matrix  will  find the right› element.  When  you  answer  for  the› bowler 1 it becomes P-1 or 1-1  or  0› so the right element is accessed. The› same is done for the game G-1 becomes› 1-1 or 0.››       ELEMENTS AND THEIR VALUES›› B(0,0)=250  B(0,1)=220  B(0,2)=240› B(1,0)=210  B(1,1)=190  B(1,2)=250› B(2,0)=240  B(2,1)=230  B(2,2)=270› B(3,0)=220  B(3,1)=200  B(3,2)=260››      You  also  can print out all the› bowling     scores     or    elements› automatically.  Please  change  lines› 130 to 180 as follows:››      130 FOR T=0 TO 2›      140 FOR K=0 TO 3›      150 ? "BOWLER ";T+1;" GAME #";›          K+1;›      160 ? " = ";B(T,K):REM<--MATRIX›      170 NEXT K›      180 NEXT T››       As   a  practical  matter  most› programmers   do  no  use  element  0› either   in  an  array  or  a  matrix› because it complicates  the  program.› DIM  the  array  or  matrix  for  the› number  of elements you have. The FOR› - NEXT loop starts with 1 instead  of› 0. See the program below.››      10 --›      20 CLS:?:?›      30 DIM B(3,4)›      40 FOR X = 1 TO 3›      50 FOR Y = 1 TO 4›      60 ? "BOWLER ";X;" GAME #";Y›      70 INPUT "SCORE PLEASE ";S›      80 B(X,Y)=S:REM <--MATRIX›      90 ?›      100 NEXT Y›      110 NEXT X›      120 PAUSE 60›      130 --›      140 ? "LET'S SEE IF IT WORKED?"›      150 FOR T = 1 TO 3›      160 FOR K = 1 TO 4›      170 ? "BOWLER ";T;" GAME #";K;›      180 ?" = ";B(T,K):REM<--MATRIX›      190 NEXT K›      200 NEXT T›››             STRING ARRAYS›             -------------››      TURBO-BASIC  and  ATARI BASIC do› not allow string arrays. This  is  no› big  problem.  We  create  a   PSEUDO› STRING ARRAY that looks and acts like› a normal string array. We take a long› string and chop it into equal pieces.› In order to create this PSEUDO STRING› ARRAY we must do certain things.››      1)Decide how many elements we›        need›      2)The length of each element›      3)Calculate the end of the›        FOR-NEXT loop and the STEP››      For example, we want to create a› string array that has 7 elements  and› each  element  is 10 letters long. We› will call the main string X$. To find› out  how  much  to DIM X$ we multiply› the  number  of  elements  times  the› length of each element (7 x 10 = 70).› We  now DIM X$(70). The FOR-NEXT loop› starts with 1 and ends with  the  DIM› in  this  case  70.  The  step is the› element length(10) 'FOR N = 1  TO  70› STEP 10››      Since  the words we put into the› string array will be shorter than  10› letters,  we  use  PAD$  which has 10› empty spaces to pad each substring or› element  so it is 10 letters long. We› can visualize this as follows:››                  X$››  -----------------------------------›  |    |    |    |    |    |    |   |›  |EL 1|EL 2|EL 3|EL 4|EL 5|EL 6|EL7|›  |    |    |    |    |    |    |   |›  -----------------------------------›  1   10   20   30   40   50   60  70››      Elements or substrings start and› end as follows:››        ELEMENTS OR SUBSTRINGS››      Element 1 =  1 to 10›      Element 2 = 11 to 20›      Element 3 = 21 to 30›      Element 4 = 31 to 40›      Element 5 = 41 to 50›      Element 6 = 51 to 60›      Element 7 = 61 to 70››      It  looks  as if each element is› only 9 letters  long.  These  numbers› are  inclusive  so  each  one  is  10› letters long››      If  we have a FOR-NEXT-STEP loop› we can generate these numbers.››      10 FOR N = 1 TO 70 STEP 10›      20 ? N, N+9›      30 NEXT N››      The result of this  loop  is  as› follows:››      1    10›      11   20›      21   30›      31   40›      41   50›      51   60›      61   70››      This  is  the  way  the  program› would  look. Please key in this short› demo program.››      10 --›      20 CLS:?:?›      30 DIM X$(70),SUB$(10),PAD$(10)›      40 PAD$="         ":REM FOR›         PADDING THE SUBSTRING 10›         SPACES›      50 REM ASSIGNING PSEUDO STRING›         ARRAY VALUES›      60 FOR N = 1 TO 70 STEP 10›      70 INPUT "GIVE ME A WORD(MAX›         10 LETTRS)";SUB$:?›      80 SL=LEN(SUB$):REM LENGTH OF›         WORD›      90 IF SL<10 THEN›         SUB$(SL+1)=PAD$:REM PAD TO›         10 LETTERS›      100 X$(N,N+9)=SUB$:REM PUT›          VALUE INTO ELEMENTS›      110 NEXT N›      120 --›      130 ?:?›      140 REM DISPLAY PSEUDO STRING ›          ARRAY›      150 FOR N=1 TO 70 STEP 10›      160 K=K+1:REM COUNTER›      170 ? "ELEMENT ";K;" = ";›          X$(N,N+9)›      180 NEXT N›      190 --››      A line by  line  explanation  of› this program is as follows:›› 10 Draw 30 dashes› 20 Clear the screen› 30 Dim X$ for the total amount of›    all the elements. The SUB$ is›    the length of an element. The›    PAD$ is the length of an element› 40 PAD$ = is the length of an›    element(10). It is used to pad›    a word that is too short - less›    than 10 letters› 50 Rem explanation› 60 FOR-NEXT-loop. It starts with 1›    and ends with the number of›    elements(7) times the length of›    each element(10) or (7x10=70).The›    step is the length of the›    element(10)› 70 INPUT the words› 80 Find out how long each word is.› 90 Pad each word to 10 characters› 100 Fill the elements or the SUB$›     with words. The sub strings or›     elements are 1-10, 11-20, 21-30,›     31-40, 41-50, 51-60, 61-70› 110 End of loop› 120 Draw 30 dashes› 130 Print› 140 Rem explanation› 150 FOR-NEXT loop. See explanation›     on line 60› 160 A counter that counts the number›     of elements in the array› 170 Print the elements in X$(N,N+9)›     The substrings or elements in X$›     are 1-10, 11-20, 21-30, 31-40,›     41-50, 51-60, 61-70› 180 End of loop› 190 Draw 30 dashes››       You    can   also   print   out› individual  elements  of  the  string› array. Please  change  the  following› lines.››      150 N = 0›      160 INPUT "WHAT ELEMENT DO YOU›          WANT TO SEE";N›      170 ? "ELEMENT ";N;" = ";›          X$(N*10-9,N*10)›      180 GOTO 150›› >>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<››