rand

Syntax

#include <stdlib.h> int rand(void);

Description

Returns a pseudo-random number between zero and RAND_MAX (defined on `stdlib.h').

By default, this function always generates the same sequence of numbers each time you run the program. (This is usually desirable when debugging, or when comparing two different runs.) If you need to produce a different sequence on every run, you must seed rand by calling srand (see section srand) before the first call to rand, and make sure to use a different argument to srand each time. The usual technique is to get the argument to srand from a call to the time library function (see section time), whose return value changes every second.

To get a random number in the range 0..N, use rand()%(N+1). Note that the low bits of the rand's return value are not very random, so rand()%N for small values of N could be not enough random. The alternative, but non-ANSI, function random is better if N is small. See section random.

Return Value

The number.

Portability

ANSI/ISO C	C89; C99
POSIX	1003.2-1992; 1003.1-2001

Example

/* random pause */ srand(time(0)); for (i=rand(); i; i--);