void srand(unsigned int seed);
srand uses the argument seed as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to rand. If srand is called with the same seed value, the same sequence of pseudo-random numbers is generated.
If rand is called before any calls to srand have been made, a sequence is generated as if srand is first called with a seed value of 1.
rand or 'ref rand_max