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Contents / Part 3 / Previous chapter / Next chapter / Index
One very common way of storing a whole set of information along with the computer program is to use DATA statements. You will remember that computer programs can be stored on cassette and sets of data can be stored in the program as well. For example it might be necessary in a program to convert the month given as a number into a name. The program below stores the names of the month as DATA
5 REPEAT
10 PRINT "GIVE THE MONTH AS A NUMBER"
20 INPUT M
30 UNTIL M>0 AND M<13
40 FOR X=1 TO M
50 READ A$
60 NEXT X
70 PRINT "THE MONTH IS ";A$
100 DATA JANUARY, FEBRUARY, MARCH, APRIL
110 DATA MAY, JUNE, JULY, AUGUST, SEPTEMBER
120 DATA OCTOBER, NOVEMBER, DECEMBER
>RUN
GIVE THE MONTH AS A NUMBER
?6
THE MONTH IS JUNE
Lines 10 to 30 repeat until a sensible value (or M is entered) - it must be between 1 and 12. In the example run a value of 6 was given to M. In this case the FOR...NEXT loop between lines 40 and 60 will go round 6 times. Each time it goes around it READs the next piece of DATA into A$ until finally A$ will be
left containing JUNE. It might make it clearer if an extra line is temporarily inserted at line 55 to print out the value of A$ and X each time around the loop.
>55PRINT A$,X
>
>LIST
5 REPEAT
10 PRINT "GIVE THE MONTH AS A NUMBER"
20 INPUT M
30 UNTIL M>0 AND N<13
40 FOR X=1 TO M
50 READ AS
55 PRINT A$,X
60 NEXT X
70 PRINT "THE MONTH IS ";A$
100 DATA JANUARY, FEBRUARY, MARCH, APRIL
110 DATA MAY, JUNE, JULY, AUGUST, SEPTEMBER
120 DATA OCTOBER, NOVEMBER, DECEMBER
>
>RUN
GIVE THE MONTH AS A NUMBER
?6
JANUARY 1
FEBRUARY 2
MARCH 3
APRIL 4
MAY 5
JUNE 6
THE MONTH IS JUNE
This is quite a neat way of getting to the (say) sixth element of a list but there is another way using an array.
Sometimes there is more than one set of data and it is useful to be able to set the 'data pointer' to a selected set of data. The next program has two sets of data each containing a set of prices and car names. One set of data refers to British Leyland cars and the other to Lotus cars.
10 REPEAT
20 PRINT "DO YOU PREFER BL OR LOTUS CARS? ";
30 A$=GET$
40 PRINT A$
50 IF A$="B" THEN RESTORE 170 ELSE RESTORE 340
60 INPUT "HOW MANY POUNDS CAN YOU AFFORD ",P
80 PRINT "YOU CAN AFFORD THESE THEN:"
90 FOR X=1 TO 15
100 READ NAME$
110 READ PRICE
120 IF PRICE <P THEN PRINT PRICE,TAB(15);NAME$
130 NEXT X
140 PRINT
150 UNTIL FALSE
160
170 REM BRITISH LEYLAND CARS
180 DATA MINI 1000 CITY, 2898
190 DATA METRO HLE, 4198
200 DATA DOLOMITE 1300,4351
210 DATA SPITFIRE 1500, 4696
220 DATA TRIUMPH ACCLAIM HLS, 4988
230 DATA ALLEGRO 31.3 HLS, 5095
240 DATA DOLOMITE 1500HL, 5225
250 DATA PRINCESS 2 HL, 5899
260 DATA DOLOMITE SPRINT, 7118
270 DATA TR7 FIXEDHEAD, 7258
280 DATA ROVER 2300, 7450
290 DATA DAIMLER SOVEREIGN 4.2, 16259
300 DATA JAGUAR XJ6 4.2,16279
310 DATA DAIMLER VANDEN PLAS 4.2, 21419
320 DATA DAIMLER LIMOUSINE, 26998
330
340 REN LOTUS CARS
350 DATA ESPRIT S3, 13513
360 DATA ECLAT SERIES 2.2, 14857
370 DATA TURBO ESPRIT, 16982
380 RATA ELITE SERIES 2.2, 17206
>RUN
DO YOU PREFER BL OR LOTUS CARS? B
HOW MANY POUNDS CAN YOU AFFORD ?10000
YOU CAN AFFORD THESE THEN:
2898 MINI 1000 CITY
4198 METRO HLE
4351 DOLOMITE 1300
4696 SPITFIRE 1500
4988 TRIUMPH ACCLAIM HLS
5095 ALLEGRO 31.5 HLS
5225 DOLOMITE 1500HL
5899 PRINCESS 2 HL
7118 DOLOMITE SPRINT
7258 TR7 FIXEDHEAD
7450 ROVER 2300
DO YOU PREFER BL OR LOTUS CARS? L
HOW MANY POUNDS CAN YOU AFFORD ?1700
YOU CAN AFFORD THESE THEN:
Out of DATA at Line 100
You will notice that line 50 uses the RESTORE statement to set the data 'pointer' to either line 170 where BL, data is stored or to line 340 where Lotus data is stored. This ensures that data is read from the correct list.
Lines 90 to 130 attempt to read off 15 sets of data from the data lists but fails when Lotus data is selected as only 4 sets of data are provided. The message
Out of DATA at Line 100
indicates the failure to kind enough entries in the data table. Methods of overcoming the problem are given in section 27 which deals with error handling.