HP HP-11C User Manual

Section 11: Programming Techniques 217
Random Numbers
The HP-11C has a convenient built-in function that generates
pseudo-random numbers ([RAN#]). By pseudo-random we mean
that no calculator or computer, no matter how powerful, can
generate a totally random number. The nature of the machine is
such that it performs a sequence of established steps on an input
and produces a predictable result. So the random number generator
on the HP-11C takes a random ‘‘seed”, stored by the user, and
performs an operation on it to produce a generally unpredictable
(by the user) result. This result is always a number between 0 and 1,
exclusive of 1.
There are several common uses for random numbers, but they are
very frequently found in game programs. This seems reasonable
because no one likes to play against a completely predictable and
redundant opponent. Submarine Hunt is a good example of such a
game. The game requires a random initial placement of the
submarine and random evasive moves.
Notice that the program requires two random integers, the x and y
coordinates, that fall between 0 and 9 inclusive. But the random
number generator only generates numbers between 0 and 1
exclusive of 1. This turns out to be no problem. Multiplying the
output of the random number generator by 10 yields numbers from
0 to 10 exclusive of 10. Taking the integer portion of this result
gives the set of whole numbers between 0 and 9 inclusive, which is
what we want. The subroutine following 9 shows the actual
keystrokes.
To illustrate the ease in which different ranges of random numbers
may be generated let’s take another example. Suppose you need a
real number between the limits 34.5 and 98.36 including the lower
bound and excluding the upper bound. The routine need only
generate values between 0 and 63.86 (98.36 - 34.50) to which the
value 34.5 will be added. This range is easily generated by
multiplying 63.86 by the output from the random number
generator.
User-Definable Keys
Among the most useful features on the HP-11C are the five user-
definable keys: [A], (B], [C], (D], and [E]. These keys are particularly
useful for three applications:
1. Storing data in specific registers (see page 213).

HP HP-11C Specifications

General

Brand	HP
Model	HP-11C
Category	Calculator
Language	English