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)

GNU                                                18 May 1995                                           RAND(3)