Commodore PET User Manual page 309

To illustrate different number ranges, change the values of M and N in line
10. For example, make M=l and N=6; this will generate an unending sequence
of random numbers between 1 and 6.
A quick scan of the display above shows that numbers repeat within the
first 100 generated. That is, every 101 numbers will not sort from -50 to +50 with
every number present and no duplications. This is fine in. say. a dice game where
Vou take the rolls as they come. For other random number uses, however, Vou
may need to develop random numbers in a certain range where every number
is accounted for and there are no duplications. An example is sorting a deck
of cards. Here vou need to pick a card, and when that card has been picked it can-
not be picked again du ring the same deal.
The program below shows one way to program shuffling a deck of cards
on the PET. It fills a 52-element table 0%* with the numbers 1 through 52 in a
random sequence. The cards can be pegged to the random numbers in any way,
such as:
A=1,
2~2. 3~3,
H'
Q~12,
K=13
Spades=O. Hearts= 13, Diamonds=26, Clubs=42
4
44
41
15
36
12
:31 49
3(1 24
42 20
33
51
36 34 .")C'
,;.._1
24
2·...
28 1
.:,.
1
.-..-.
37 :~:
.:,
.
.::.
16
11
6 10
5 21
13
46
32
9 :3
(1
4(1
29
With this scheme the Ace of Spades = 1+0= 1, the Queen of Spades=12+0=12,
The Three of Hearts=3+ 13=16. etc.
ln the shuffle program, a 52-element flag table FL keeps track of whether a
card has been picked or not. PRINT statements are inserted to print out the seed
value, followed by the numbers in a continuous-line format. Note that exactly 52
numbers are printed out and that no number is repeated. Each program run will
produce a new random sequence.
10 D1M FL(52»D~(52)
20 X=RND(-T1):PR1NT X
3(1 FOI<: 1=1 TO 52
40 C~=52*I<:ND(1)+1
5(1 IF FL
(c;,~) O(l~
GOTO 40
60 D~(1)=C~:FL(C~)=l
7(1 PR l NT C;~ .;
8(1
t'~EXT
l
RUN
1. 18586613E-05
48 40 13 37 50 43
23 38 25 11 9 35
26 5 6 1 45 10 21 14
34 18 52 47 7 16 8 19
17 3 22 27 29 28 39 2
F.:UN
1. 01154728E-06
14 35 52 50 26 48 27
18 20 41 33 39 7 46
12 43 2 31 44 4
22
45 48
42 49
9 51 17 8 15 38
"Element 0 is not used.
296