11-25-2008
Are you posting homework assignments? Why do you need different random numbers from 1 to 18?
There are 2 ways:
1/ keep generating random numbers, reject the ones you already have (use a hash to store them) until you have enough different ones
-> This creates a lot of extra work, and if you want more random numbers than available in your range, you'll get an infinite loop. Worst-case execution time is unpredictable (averages can be calculated with use of statistics)
2/ Generate an array of "accepted values" and pick a random element from the array, then remove it from the array.
-> Nice & fast if you got a small range, predictable worst-case scenario
If you want me to write out the script, take a minute to explain why you need it. If it's for homework, we won't solve it for you. We'll help you think and we'll look at your scripts and find mistakes, but won't write the whole thing for you.
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LEARN ABOUT REDHAT
random
RANDOM(3) Linux Programmer's Manual RANDOM(3)
NAME
random, srandom, initstate, setstate - random number generator.
SYNOPSIS
#include <stdlib.h>
long int random(void);
void srandom(unsigned int seed);
char *initstate(unsigned int seed, char *state, size_t n);
char *setstate(char *state);
DESCRIPTION
The random() function uses a non-linear additive feedback random number generator employing a default table of size 31 long integers to
return successive pseudo-random numbers in the range from 0 to RAND_MAX. The period of this random number generator is very large, approx-
imately 16*((2**31)-1).
The srandom() function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by random(). These
sequences are repeatable by calling srandom() with the same seed value. If no seed value is provided, the random() function is automati-
cally seeded with a value of 1.
The initstate() function allows a state array state to be initialized for use by random(). The size of the state array n is used by init-
state() to decide how sophisticated a random number generator it should use -- the larger the state array, the better the random numbers
will be. seed is the seed for the initialization, which specifies a starting point for the random number sequence, and provides for
restarting at the same point.
The setstate() function changes the state array used by the random() function. The state array state is used for random number generation
until the next call to initstate() or setstate(). state must first have been initialized using initstate() or be the result of a previous
call of setstate().
RETURN VALUE
The random() function returns a value between 0 and RAND_MAX. The srandom() function returns no value. The initstate() and setstate()
functions return a pointer to the previous state array, or NULL on error.
ERRORS
EINVAL A state array of less than 8 bytes was specified to initstate().
NOTES
Current "optimal" values for the size of the state array n are 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to the
nearest known amount. Using less than 8 bytes will cause an error.
CONFORMING TO
BSD 4.3
SEE ALSO
rand(3), srand(3)
GNU
2000-08-20 RANDOM(3)