The first version of the program above randomly fills the screen
with
the
keyed-in character.
It
does this by simply POKEing to random screen locations.
It
may
POKE
many times to the same location when other locations
are
not
yet
filled, and
it
continues to
POKE
even after the screen
is
filled until a new character
is
keyed
in.
When
the program
is
run, about half the screen positions quickly fill
with
the character. Then character placement slows
down
more and more until at the
end, when the screen
is
almost filled, and remaining positions are filled very
slowly.
It
takes about three minutes to completely fill the screen
with
this version
of the program.
The program
is
operating at the same speed throughout.
but
it doesn't get
much
work
done towards the end because many of the positions that it
POKEs
to
are already filled. The program appears to slow
down
because a
POKE
(or
PRINT)
of a character over the same character has no visible effect.
The program can
be
speeded up a good deal by eliminating the superfluous
POKEs
to screen positions
that
are already fi lied. A new version of program
BLANKET does this.
Rather than calculating a number in the same range ail the time and discard-
ing, or in this case re-POKEing, the duplicate numbers, the new program
decreases the range of numbers generated to correspond
with
the number of
items left to operate
on.
It
does this by keeping track of the screen positions
re-
maining to
be
filled in a table and generating a random number
within
the range
of table indexes yet to
be
POKEd
to.
The
POKE
address itself
is
gotten from the
contents at the table index.
5
REM
RANDOM
VERSION 2
10
REM
~*****~
B
LAN
K E T
*~*~~**
2(1
RE!'1
RANDOM
DISPLAY
OF
ONE
30
REM
CHARACTER
ENTERED
FROM
THE
40
REM
KEYBOARD
50
REM
*****~~~***~**************~****
70
DIM
T(999)
80
GOSUB
200
:REM
INITIALIZE
TABLE
9(1
PRINT"HIT
A
KEY
OR
<:R:>
TO
END
Il
;
1(10
GET
C$:IF
C$=""
GOTO
100
1(15
IF
C$=CHR$(13)
GOTO
170
110
PR
1
tH
":']"
.;
:
REM
CLEA!':
SCREEt"
120
X=RND
( -
TI)
:
REM
STA!':T
NEW
SEEII
125
C=(ASC(C$)At'Œ128)/2
OF:
(ASC(C$)AND63)
126
FOR
N=999
Ta
0 STEP
-1
127
A~=(N+1)*RND(1)
:REM
PICK
AN
ELEM
128
A=T(A~)+32768
:REM
FORM
POKE
AD
DR
129
TP=T(A;O:
T(A;':)=T(tü:
T(t-D=TP:
REM
S~.JAP
ELEME~nS
130
POKE
A.C
:REM
DISPLAY
CHAR
140
NE~~T
t"
160
GOTO
100
170
ENI'
199
REM
**SUBR
TO
INITIALIZE
TABLE~*
200
FOR
1=(1
Ta
999:T(!)=I:NEXT
210
RETURN
298
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