ZX Computings - OpenLibra

BASIC PROGRAM
5 LET Z = 1 + PEEK 16396
+ 256 * PEEK 16397
100 POKE Z + 726,128
150 LET AS = INKEY$
160 IF A$
"9" THEN GOTO 10
170 LET A = VAL A$
180 FOR B = 693 TOO STEP
- 33
200 POKE Z + B,23
210 LET B = B + A*0.16
220 NEXT B
320 GOTO 110
(Run using KEYS 0 to 9 to fire)
Now we have the problem of
rubbing out the stars (*) after
each shot. Try:- 300 CLS 320
GOTO 100. This rubs out the
"fire" line backwards, not
such a good idea. Try:- LIST
1 80, EDIT, change line
number to 230, N/L (new
line). LIST 200, EDIT, change
line number to 240 and
change 23 (CHR$ being
poked) to 0, N/L. LIST 210,
EDIT, change line number to
250, N/L. LIST 220, EDIT,
change line number to 260,
N/L. Then add:- 320 GOTO
1 50 AND 300 N/L.
Running the program, now
plots the gun fire, followed
immediately by plotting blank
spaces in the same positions,
using the same routine. This
solution is acceptable though
in my opinion it makes the
whole firing routine too long,
doubling up the time involved
per shot.
It was therefore decided to
try blanking out the fire one
step behind leaving only one
" * " printed at any one time.
Try this:- 230, N/L, 240, N/L,
250, N/L, 260 N/L, (to rub out
the last effort). Add lines:-1 90
POKE (B< 693)*Z + B + 33 -
A*0.16,0 followed by N/L.
Then EDIT, change the line
number to 230 and rub out
(B