The function for generating the dice rolls does a simple modulus calculation, as shown below:

int
RollDie (void)
{
  return ((rand () % 6) + 1);
}

However, this isn't really a good way to generate a random number. The low order bits aren't very 'random' in a linear congruential generator and if RAND_MAX doesn't divide evenly into 6 the distribution won't even be uniform.

Another method would be:

int
RollDie (void)
{
  double r = rand() * (1.0 / RAND_MAX);
  return (int)floor(r *6.0) + 1;
}