产生特定范围内的随机数

// Generate a random number in the half-closed interval
// [range_min, range_max). In other words,
// range_min <= random number < range_max
int get_rand(int range_min, int range_max)
{
    return (int)((double)rand() / (RAND_MAX + 1) * (range_max - range_min)
        + range_min);
}