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 <<<<<<<<<<<<<<<<¢¢
