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NAME

       rand, srand - random number generator.

SYNOPSIS

       #include <stdlib.h>

       int rand(void);

       void srand(unsigned int 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:
              "If  you want to generate a random integer between 1 and 10, you
              should always do it by using high-order bits, as in

                     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)