The rand() function returns a random integer between zero and the maximum random value for the system, which you can determine by using getrandmax() . Optional arguments can be used to limit the range of the returned value, as long as rmax is less than or equal to the value returned by getrandmax() . To maximize the randomness of the returned value, it's always a good idea - but not essential - to seed the random number generator using srand() . If one argument is passed, both arguments must be passed; otherwise, the call will generate a warning.
Note that the mt_rand() function, which uses the Mersenne Twister algorithm to generate random numbers, is usually preferable - it's faster and has known characteristics.
PHP Functions Essential Reference. Copyright © 2002 by New Riders Publishing (Authors: Zak Greant, Graeme Merrall, Torben Wilson, Brett Michlitsch). This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/). The authors of this book have elected not to choose any options under the OPL. This online book was obtained from http://www.fooassociates.com/phpfer/ and is designed to provide information about the PHP programming language, focusing on PHP version 4.0.4 for the most part. The information is provided on an as-is basis, and no warranty or fitness is implied. All persons and entities shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from the information contained in this book.