Commodore PET User Manual page 312

ln this program, lines 5 through 50 are the standard header. The Table T,
used to hold the 1000 screen position indicators, is dimensioned in line 70.
At line 80 an initialization subroutine is called that places the numbers
a
through 999 into corresponding elements of Table 1. T(O) will contain 0, T(l) will
contain 1, ... T(999) will contain 999. The elements would not have to be filled
with consecutive numbers since they are to be picked randomly, but this is the
easiest way to program the fililoop. In fact. the table will be in order only the first
time the program is run after loading. Lnes 90 through 125 are exactly the same
as in the earlier version.
Lines 126 through 140 form a FOR... NEXT loop for filling the 1000 screen
locations with the keyed-in character. Line 127 picks a random table index
A%from theremaining unfilled range of
a
to N. The formula (N+l)*RND(l) is taken
from the boxed formulas given earlier. Line 128 forms the POKE address A as the
sum of the T table element whose index was picked by line 12/, plus the begin-
ning screen memory address of 32768. Line 129 exchanges the picked table ele-
ment T(A %) with the highest active table element T(N) via a temporary location
TP. Line 130 displays the character at the random screen location. The NEXT N at
line 140 decrements the pointer N
50
that the used screen address just swapped
into T(N) is not picked again during the current program run.
5 REM RANDOM VERSION 2A
10 REM ******* B LAN K E T *******
20 REM RANDOM DISPLAY OF ONE
30 REM CHARACTER ENTERED FROM THE
40 REM KEYBOARD
50 REM *******************************
70 DIM T1(249).T2C249).T3C249).T4(249)
75 T=4 :REM NUMBER OF TABLES
76 N=250 :
F~EM
NO OF ELEr1ENTS
80 GOSUB 200 :REM INITIALIZE TABLES
90 PRINT"HIT A KE'T' OF~ <F~> TO Et·m".:
95 Nl=N:N2=N:N3=N:N4=N
1(1(1 GET C$: IF C$="" GOTO 100
105 IF C$=CHR$(13) GOTO 170
11 (1 PF: 1tH" :T' .; : REr1 CLEAF: SCREEN
120 X=RNDC-TI) :REM START NEW SEED
125 C=(ASCCC$)AND128)/2 OR (ASCCC$)AND63)
126 FOR L=lT01000 :REM 1 FOR EACH SPOT
127
n~=T*RND
( 1 ) + 1 : REr1 PI CK A TABLE
128 ON T% GOSUB 300.400,500.600 :REM GO PICK AN ELEMENT
130 POKE A.C :REM DISPLAY CHAR
140
~IE>'::T
L
160 GOTO 95
170 END
199 RErl **SU:E:F~ TO ItH TI ALI ZE TABLES**
200 FOR 1=0 TO N-l:T1CI)=I:NEXT
210 FOR
I~0
TO N-l:T2CI)=I+250:NEXT
220 FOR
I~0
TO N-l:T3CI)=I+500:NEXT
230 FOR 1=0 TO N-l ·T4(I)=I+750:NEXT
24(1
RETURt~
299 REM **SUBROUTINE FOR TABLE Tl**
299