Micro­power

Program lines similar to the following have been included in many simple computer-based learning tests.

10 READ A$, B$
20 PRINT "What is the capital of";A$
30 INPUT C$
40 IF C$=B$ THEN PRINT "Correct": GOTO 10
50 PRINT "Hard Luck -Try again":GOTO 20
60 DATA SCOTLAND, EDINBURGH, EIRE, DUBLIN
70 DATA FRANCE, PARIS, WEST GERMANY, BONN

Obviously one would enlarge on the program, with random or sequential testing, some system of marking results and suitable messages to ‘humanise’ the exercise.

It is self-evident that the basic formula using READ, DATA & RESTORE can be adopted in all such programs.

SET, RESET, POINT

As everyone will know by now, the basic Nascom screen has 16 lines of 48 characters – i.e. 768 screen locations into which you can PRINT or POKE any of the character set. The commands SET, RESET & POINT give you control of a much higher number of smaller areas on the screen. In effect, each character space is divided into 6 (2 horizontal x 3 vertical), and each ‘pixel’ as they are called, can then be turned on or off by SET and RESET. This gives and effective screen resolution of 96 x 48; computer manufacturers have been known to refer to this as ‘high resolution graphics), but this term should really be reserved for the much higher resolution obtainable with bit-mapped graphics or with a programmable character generator. As an illustration, we can randomly set all the pixels thus:

10 CLS
20 REM * SET X TO A RANDOM NO. BETWEEN 0 AND 47
30 X=INT(RND(1)*47)
40 REM* SET Y IN RANGE 0 - 95
50 Y=INT(RND(1)*95)
60 SET(X,Y) : GOTO 20

Eventually the screen would be composed entirely of ‘set’ pixels. Now we can use RESET in a similar fashion. First remove the ‘GOTO 20’ in line 60 and then enter:

70 REM * NOW DO A RANDOM RESET
80 X=INT(RND(1)*47)
90 Y=INT(RND(1)*95)
100 RESET (X,Y) : GOTO 20

The pixels will now be randomly reset. To complete the program we could use POINT to test whether certain pixels had been set, and if so start at the beginning again. Remove the ‘GOTO 20’ in line 100 and then enter: