void randomSeed(unsigned int seed)
randomSeed() configures the pseudo-random number generator with a new base value to start generating random numbers from. Without using this the generated random numbers will follow a predictable pattern.
None
randomSeed() conforms to the Arduino 1.6.x API.
Seed the random number generator from white noise from a floating analog input:
randomSeed(analogRead(A0));
int rnum = random(0, 10);