srand is used to set the seed for the random number generator
routines in rand. With no arguments, srand resets the
seed value to the last value which was set, or to 1, which is the
seed value on startup, if it hasn't been set since. If a scalar
argument is provided, it becomes the new seed. If the string
"clock" is used as the argument, the seed is set from the
internal clock. The latter method will provide unique values.