Commodore PET User Manual page 306

range 0 ta n
range 1 ta n
range m ta n
Ta generate different random numbers at each RND use. vou need ta have
same way of generating a random seed.
(y
ou can't cali RND ta doit!) A convenient
way of getting a pseudo-random seed on the PET is ta use the current jiffy count.
TI:
10 X=RND(-TI): REM START SEED
Here vou will get a different random sequence started each time statement
lOis executed.
A more nearly pure random seed* can be obtained by using RND (-RND(O)).
For example:
10 X=RND(-RND(0» REM START SEED
Here again vou will get a different random sequence started each time statement
lOis executed.
ln the programs that follow. -TI is used. as it is compatible with bath old and
new ROMs. If vou have the new ROMs. vou can use -RND(O) in place of -TI.
Vou will have to convert the random number, which is returned as a
number between 0 and 1, to whatever range you want the random number to
be in. Say vou want numbers from 1 ta 6 (as in one die number of a dice game).
You will need ta multiply the random number by 6:
6:4ERND(1)
This gives a floating point number in a range just greater than
0
but just less than
6 (O<n<6). Add 1 ta get a number in the range 1 <n<7:
6:4ERND( 1)+1
Then convert the number ta integer. which discards any fractional part of a num-
ber. returning the number ta the range
1
ta 6 but in integer form:
ItH<6:4ERND( 1)+1)
or
A;' ; :=6:4ERt·jIJ ( 1) +1
The general cases for converting the RND fraction to whole number
ranges are shown below. Note that with the INT function. these formulas handle
numbers in the integer range ±32767.
INT((n+1)'RND(1))
INT(n·RND(1)+ 1)
INT((n-m+1 );RND(1 Hm
The formulas for ranges beginning at 0 or 1 are just simplified versions
derived directly from the general case of range m ta n:
where m=O
where m=1
INT((n-m+1 )·RND(1 )+m)
INT((n-O+ 1)'RND(1 )+0)
INT((n+1).RND(1)) as shawn above
INT((n-m+ 1)·RND(1 Hm)
INT(n-1+1)·RND(1)+1)
INT(n.RND(1)+1) as shawn above
'according to the PET manufacturer
293