APPENDIX D

Example programs

This appendix contains some example programs to demonstrate the abilities of the ZX Spectrum.

The first of these programs requires a date to be input and gives the day of the week which corresponds to this date.


	10 REM convert date to day 
	20 DIM d$(7,6): REM days of week 
	30 FOR n=1 TO 7: READ d$(n): NEXT n 
	40 DIM m(12): REM lengths of months 
	50 FOR n=1 TO 12: READ m(n): NEXT n 
	100 REM input date 
	110 INPUT "day?";day 
	120 INPUT "month?";month 
	130 INPUT "year (20th century only)?";year 
	140 IF year<1901 THEN PRINT "20th century starts at 1901": GO TO 100 150 IF YEAR>2000 THEN PRINT "20th century ends at 2000": GO TO 100 
	160 IF month<1 THEN GO TO 210 170 IF MONTH>12 THEN GO TO 210 
	180 IF year/4-INT(year/4)=0 THEN LET m(2)=29: REM leap year 
	190 IF day>m(month) THEN PRINT "This month has only "; m(month);
	         " days.": GO TO 500 
	200 IF day>0 THEN GO TO 300 
	210 PRINT "Stuff and nonsense. Give me a real date." 
	220 GO TO 500 
	300 REM convert date to number of days since start of century 
	310 LET y=year-1901 
	320 LET b=365*y+INT (y/4): REM number of days to start of year 
	330 FOR n=1 TO month 1: REM add on previous months 
	340 LET b=b+m(n): NEXT n 
	350 LET b=b+day 
	400 REM convert to day of week 
	410 LET b=b-7*INT (b/7)+1 
	420 PRINT day;"/";month;"/";year 
	430 FOR n=6 TO 3 STEP -1: REM remove trailing spaces 
	440 IF d$(b,n) <> " " THEN GO TO 460 
	450 NEXT n
	460 LET e$=d$(b, TO n)
	470 PRINT" is a "; e$; "day"
	500 LET m(2)=28: REM restore February
	510 INPUT "again?", a$
	520 IF a$="n" THEN GO TO 540
	530 IF a$ <> "N" THEN GO TO 100
	1000 REM days of week
	1010 DATA "Mon", "Tues", "Wednes"
	1020 DATA "Thurs", "Fri", "Satur", "Sun"
	1100 REM lengths of months
	1110 DATA 31, 28, 31, 30, 31, 30
	1120 DATA 31, 31, 30, 31, 30, 31

This program handles yards, feet and inches.


	10 INPUT "yards?",yd,"feet?",ft, "inches?",in
	40 GO SUB 2000: REM print the values
	50 PRINT '" = ";
	70 GO SUB 1000: REM the adjustment
	80 GO SUB 2000: REM print the adjusted values
	90 PRINT
	100 GOTO 10
	1000 REM subroutine to adjust yd, ft, in to the normal form for yards, 
	            feet and inches
	1010 LET in=36*yd+12*ft+in: REM now everything is in inches
	1030 LET s=SGN in: LET in=ABS in: REM we work with in positive, 
	            holding its sign in s
	1060 LET ft=INT (in/12): LET in=(in-12*ft)*s: REM now in is ok
	1080 LET yd=INT (ft/3)*s: LET ft=ft*s-3*yd: RETURN
	2000 REM subroutine to print yd, ft and in
	2010 PRINT yd;"yd";ft;"ft";in;"in";: RETURN 

Here is a program to throw coins for the I Ching. (Unfortunately it produces the patterns upside down. but you might not worry about this.)


	5 RANDOMIZE 
	10 FOR m=1 TO 6: REM for 6 throws 
	20 LET c=0: REM initialize coin total to 0 
	30 FOR n=1 TO 3: REM for 3 coins 
	40 LET c=c+2+INT (2*RND) 
	50 NEXT n 60: PRINT " "; 
	70 FOR n=1 TO 2: REM 1st for the thrown hexagram, 2nd for the changes 
	80 PRINT "___";
	90 IF c=7 THEN PRINT " "; 
	100 IF c=8 THEN PRINT " "; 
	110 IF c=6 THEN PRINT "X";: LET c=7 
	120 IF c=9 THEN PRINT "0";: LET c=8
	130 PRINT "___ ";
	140 NEXT n
	150 PRINT
	160 INPUT a$
	170 NEXT m: NEW

To use this, type it in and run it, and then press ENTER five times to get the two hexagrams. Look these up in a copy of the Chinese Book of Changes. The text will describe a situation and the courses of action appropriate to it, and you must ponder deeply to discover the parallels between that and your own life. Press ENTER a sixth time, and the program will erase itself this is to discourage you from using it frivolously.

Many people find the texts are always more apt than they would expect on grounds of chance; this may or may not be the case with your ZX Spectrum In general, computers are pretty godless creatures.

Here is a program to play 'Pangolins'. You think up an animal, and the computer tries to guess what it is, by asking you questions that can be answered 'yes' or 'no'. If it's never heard of your animal before, it asks you to give it some question that it can use next time to find out whether someone's given it your new animal.


	5 REM Pangolins
	10 LET nq=100: REM number of questions and animals
	15 DIM q$(nq,50): DIM a(nq,2): DIM r$(1)
	20 LET qf=8
	30 FOR n=1 TO qf/2 1
	40 READ q$(n): READ a(n,1): READ a(n,2)
	50 NEXT n
	60 FOR n=n TO qf-1
	70 READ q$(n): NEXT n
	100 REM start playing
	110 PRINT "Think of an animal.","Press any key to continue."
	120 PAUSE 0
	130 LET c=1: REM start with 1st question
	140 IF a(c,1)=0 THEN GO TO 300
	150 LET p$=q$(c): GO SUB 910
	160 PRINT "?": GO SUB 1000
	170 LET in=1: IF r$="y" THEN GO TO 210
	180 IF r$="Y" THEN GO TO 210
	190 LET in=2: IF r$="n" THEN GO TO 210
	200 IF r$<>"N" THEN GO TO 150
	210 LET c=a(c,in): GO TO 140
	300 REM animal
	310 PRINT "Are you thinking of"
	320 LET P$=q$(c): GO SUB 900: PRINT "?"
	330 GO SUB 1000
	340 IF r$="y" THEN GO TO 400
	350 IF r$="Y" THEN GO TO 400
	360 IF r$="n" THEN GO TO 500
	370 IF r$="N" THEN GO TO 500
	380 PRINT "Answer me properly when I'm","talking to you.": GO TO 300
	400 REM guessed it
	410 PRINT "I thought as much.": GO TO 800
	500 REM new animal 
	510 IF qf>nq-1 THEN PRINT "I'm sure your animal is very", "interesting, 
	         but I don't have","room for it just now.": GO TO 800 
	520 LET q$(qf)=q$(c): REM move old animal 
	530 PRINT "What is it, then?": INPUT q$(qf+1) 
	540 PRINT "Tell me a question which dist ","inguishes between " 
	550 LET p$=q$(qf): GO SUB 900: PRINT " and" 
	560 LET p$=q$(qf+1): GO SUB 900: PRINT " " 
	570 INPUT s$: LET b=LEN s$ 
	580 IF s$(b)="?" THEN LET b=b-1 
	590 LET q$(c)=s$(TO b): REM insert question 
	600 PRINT "What is the answer for" 
	610 LET p$=q$(qf+1): GO SUB 900: PRINT "?" 
	620 GO SUB 1000 
	630 LET in=1: LET io=2: REM answers for new and old animals 
	640 IF r$="y" THEN GO T0 700 
	650 IF r$="Y" THEN GO TO 700 
	660 LET in=2: LET io=1 
	670 IF r$="n" THEN GO TO 700 
	680 IF r$="N" THEN GO TO 700
	690 PRINT "That's no good. ": GO TO 600
	700 REM update answers 
	710 LET a(c,in)=qf+1: LET a(c,io)=qf 
	720 LET qf=qf+2: REM next free animal space 
	730 PRINT "That fooled me."
	800 REM again?
	810 PRINT "Do you want another go?": GO SUB 1000
	820 IF r$="y" THEN GO TO 100
	830 IF r$="Y" THEN GO TO 100
	840 STOP
	900 REM print without trailing spaces
	905 PRINT " ";
	910 FOR n=50 TO 1 STEP -1
	920 IF p$(n)<>" " THEN GO TO 940
	930 NEXT n
	940 PRINT p$(TO n);: RETURN
	1000 REM get reply
	1010 INPUT r$: IF r$="" THEN RETURN
	1020 LET r$=r$(1): RETURN
	2000 REM initial animals
	2010 DATA "Does it live in the sea",4,2
	2020 DATA "Is it scaly",3,5
	2030 DATA "Does it eat ants",6,7
	2040 DATA "a whale", "a blancmange", "a pangolin", "an ant"

Here is a program to draw a Union Flag.


	5 REM union flag
	10 LET r=2: LET w=7: LET b=1
	20 BORDER 0: PAPER b: INK w: CLS
	30 REM black in bottom of screen
	40 INVERSE 1
	50 FOR n=40 TO 0 STEP -8
	60.PLOT PAPER 0;7,n: DRAW PAPER 0;241,0
	70 NEXT n: INVERSE 0
	100 REM draw in white parts
	105 REM St. George
	110 FOR n=0 TO 7
	120 PLOT 104+n,175: DRAW 0,-35
	130 PLOT 151-n,175: DRAW 0,-35
	140 PLOT 151-n,48: DRAW 0,35
	150 PLOT 104+n,48: DRAW 0,35
	160 NEXT n
	200 FOR n=0 TO 11
	210 PLOT 0,139-n: DRAW 111,0
	220 PLOT 255,139-n: DRAW  111,0
	230 PLOT 255,84+n: DRAW -111,0
	240 PLOT 0,84+n: DRAW 111,0
	250 NEXT n
	300 REM St. Andrew
	310 FOR n=0 TO 35
	320 PLOT 1+2*n,175-n: DRAW 32,0
	330 PLOT 224-2*n,175-n: DRAW 16,0
	340 PLOT 254-2*n,48+n: DRAW-32,0 
	350 PLOT 17+2*n,48+n: DRAW 16,0
	360 NEXT n
	370 FOR n=0 TO 19
	380 PLOT 185+2*n,140+n: DRAW 32,0 
	390 PLOT 200+2*n,83-n: DRAW 16,0
	400 PLOT 39-2*n,83-n: DRAW 32,0
	410 PLOT 54-2*n,140+n: DRAW -16,0
	420 NEXT n
	425 REM fill in extra bits 
	430 FOR n=0 TO 15
	440 PLOT 255,160+n: DRAW 2*n-30,0 
	450 PLOT 0,63-n DRAW 31-2*n,0
	460 NEXT n
	470 FOR n=0 TO 7
	480 PLOT 0,160+n: DRAW 14 2*n,0
	485 PLOT 255,63-n: DRAW 2*n-15,0 
	490 NEXT n
	500 REM red stripes 
	510 INVERSE 1
	520 REM St George
	530 FOR n=96 TO 120 STEP 8
	540 PLOT PAPER r;7,n: DRAW PAPER r;241,0 
	550 NEXT n
	560 FOR n=112 TO 136 STEP 8
	570 PLOT PAPER r;n,168: DRAW PAPER r;0,-113 
	580 NEXT n
	600 REM St Patrick
	610 PLOT PAPER r;170,140: DRAW PAPER r;70,35 
	620 PLOT PAPER r;179,140: DRAW PAPER r;70,35 
	630 PLOT PAPER r;199,83: DRAW PAPER r;56,-28 
	640 PLOT PAPER r;184,83: DRAW PAPER r;70,-35 
	650 PLOT PAPER r;86,83: DRAW PAPER r;-70,-35 
	660 PLOT PAPER r;72,83: DRAW PAPER r;-70,-35 
	670 PLOT PAPER r;56,140: DRAW PAPER r;-56,28 
	680 PLOT PAPER r;71,140: DRAW PAPER r;-70,35 
	690 INVERSE 0: PAPER 0: INK 7

If you're not British, have a go at drawing your own flag. Tricolours are fairly easy, although some of the colours - for instance the orange in the Irish flag - might present difficulties. If you're an American, you might be able to fit the character * in.

Here is a program to play hangman. One player enters a word, and the other guesses


	5 REM hangman 
	10 REM set up screen 
	20 INK 0: PAPER 7: CLS 
	30 LET x=240: GO SUB 1000: REM draw man 
	40 PLOT 238,128: DRAW 4,0: REM mouth 
	100 REM set up word 
	110 INPUT w$: REM word to guess 
	120 LET b=LEN w$: LET v$=" " 
	130 FOR n=2 TO b: LET v$=v$+" " 
	140 NEXT n: REM v$=word guessed so far 
	150 LET c=0: LET d=0: REM guess & mistake counts 
	160 FOR n=0 TO b-1 
	170 PRINT AT 20,n;" ";
	180 NEXT n: REM write  's instead of letters
	200 INPUT "Guess a letter ";g$ 
	210 IF g$="" THEN GO TO 200 
	220 LET g$=g$(1): REM 1st letter only 
	230 PRINT AT 0,c;g$ 
	240 LET c=c+1: LET u$=v$ 
	250 FOR n=1 TO bL REM update guessed word 
	260 IF w$(n)=g$ THEN LET v$(n)=g$ 
	270 NEXT n 
	280 PRINT AT l9,0;v$ 
	290 IF v$=w$ THEN GO TO 500: REM word guessed 
	300 IF v$<>u$ THEN GO TO 200: REM guess was right 
	400 REM draw next part of gallows 
	410 IF d=8 THEN GO TO 600: REM hanged 
	420 LET d=d+1
	430 READ x0,y0,x,y 
	440 PLOT x0,y0: DRAW x,y 
	450 GO TO 200 
	500 REM free man 
	510 OVER 1: REM rub out man 
	520 LET x=240: GO SUB 1000 
	530 PLOT 238,128: DRAW 4,0: REM mouth 
	540 OVER 0: REM redraw man 
	550 LET x=146: GO SUB 1000 
	560 PLOT 143,129: DRAW 6,0, PI/2: REM smile 
	570 GO TO 800 
	600 REM hang man 
	610 OVER 1: REM rub out floor 
	620 PLOT 255,65: DRAW -48,0
	630 DRAW 0,-48: REM open trapdoor
	640 PLOT 238,128: DRAW 4,0: REM rub out mouth
	650 REM move limbs
	655 REM arms
	660 PLOT 255,117: DRAW -15,-15: DRAW -15,15
	670 OVER 0
	680 PLOT 236,81: DRAW 4,21: DRAW 4, 21
	690 OVER 1: REM legs
	700 PLOT 255,66: DRAW -15,15: DRAW -15,-15
	710 OVER 0
	720 PLOT 236,60: DRAW 4,21: DRAW 4,-21
	730 PLOT 237,127: DRAW 6,0,-PI/2: REM frown
	740 PRINT AT 19,0;w$
	800 INPUT "again? ";a$
	810 IF a$="" THEN GO TO 850
	820 LET a$=a$(1)
	830 IF a$="n" THEN STOP
	840 IF a$(1)="N" THEN STOP
	850 RESTORE: GO TO 5
	1000 REM draw man at column x
	1010 REM head
	1020 CIRCLE x,132,8
	1030 PLOT x+4,134: PLOT x-4,134: PLOT x,131
	1040 REM body
	1050 PLOT x,123: DRAW 0,-20
	1055 PLOT x,101: DRAW 0,-19
	1060 REM legs
	1070 PLOT x-15,66: DRAW 15,15: DRAW 15,-15
	1080 REM arms
	1090 PLOT x-15,117: DRAW 15,-15: DRAW 15,15
	1100 RETURN
	2000 DATA 120,65,135,0,184,65,0,91
	2010 DATA 168,65,16,16,184,81,16,-16
	2020 DATA 184,156,68,0,184,140,16,16
	2030 DATA 204,156,-20,-20,240,156,0,-16
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