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RAND
!!!RAND
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
NOTES
CONFORMING TO
SEE ALSO
----
!!NAME


rand, srand - random number generator.
!!SYNOPSIS


__#include
__ ''seed''__);
__
!!DESCRIPTION


The __rand()__ function returns a pseudo-random integer
between 0 and __RAND_MAX__.


The __srand()__ function sets its argument as the seed
for a new sequence of pseudo-random integers to be returned
by __rand()__. These sequences are repeatable by calling
__srand()__ with the same seed value.


If no seed value is provided, the __rand()__ function is
automatically seeded with a value of 1.
!!RETURN VALUE


The __rand()__ function returns a value between 0 and
RAND_MAX. The __srand()__ returns no value.
!!NOTES


The versions of __rand()__ and __srand()__ in the
Linux C Library use the same random number generator as
__random()__ and __srandom()__, so the lower-order
bits should be as random as the higher-order bits. However,
on older __rand()__ implementations, the lower-order bits
are much less random than the higher-order
bits.


In ''Numerical Recipes in C: The Art of Scientific
Computing'' (William H. Press, Brian P. Flannery, Saul A.
Teukolsky, William T. Vetterling; New York: Cambridge
University Press, 1992 (2nd ed., p. 277)), the following
comments are made:




j=1+(int) (10.0*rand()/(RAND_MAX+1.0));


and never by anything resembling


j=1+(rand() % 10);


(which uses lower-order bits).


Random-number generation is a complex topic. The
''Numerical Recipes in C'' book (see reference above)
provides an excellent discussion of practical random-number
generation issues in Chapter 7 (Random
Numbers).


For a more theoretical discussion which also covers many
practical issues in depth, please see Chapter 3 (Random
Numbers) in Donald E. Knuth's ''The Art of Computer
Programming'', volume 2 (Seminumerical Algorithms), 2nd
ed.; Reading, Massachusetts: Addison-Wesley Publishing
Company, 1981.
!!CONFORMING TO


SVID 3, BSD 4.3, ISO 9899
!!SEE ALSO


random(3), srandom(3), initstate(3),
setstate(3)
----

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Last edited on Tuesday, June 4, 2002 12:24:31 am by "perry"

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