How do I scale down numbers from rand()?

If you are using C++ and are concerned about good distribution you can use TR1 C++11 <random>.

#include <random>

std::random_device rseed;
std::mt19937 rgen(rseed()); // mersenne_twister
std::uniform_int_distribution<int> idist(0,100); // [0,100]

std::cout << idist(rgen) << std::endl;