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)