int rand ([int min [, int max]])
If called without the optional min, max arguments rand() returns a pseudo-random value between 0 and RAND_MAX. If you want a random number between 5 and 15 (inclusive), for example, use rand (5, 15).
Remember to seed the random number generator before use with srand().
Note: In versions before 3.0.7 the meaning of max was range. To get the same results in these versions the short example should be rand (5, 11) to get a random number between 5 and 15.
See also srand(), getrandmax(), mt_rand(), mt_srand(), and mt_getrandmax().