The <random> library C++ code has a modern library <random> that improves over the old C and C++ use of rand() found in <cstdlib>. In the program that we saw in week 1 for calculating the probabilities when rolling two dice:
//The following program computes
//the probability for dice possibilities
#include <iostream> //drops .h still available
#include <cstdlib>
#include <ctime>
using namespace std;
const int sides = 6; //replaces many sharp defines
inline int r_sides(){ return (rand() % sides + 1); }
int main(void)
{
const int n_dice = 2;
srand(clock()); //why?
cout << "\nEnter number of trials: ";
int trials;
cin >> trials; //compare to scanf
int* outcomes = new int[n_dice * sides +1];
for (int j = 0; j < trials; ++j) {
int roll = 0;
for (int k = 1; k <= n_dice; ++k) {
roll += r_sides();
}
outcomes[roll]++;
}
cout << "probability\n";
for (int j = 2; j < n_dice * sides + 1; ++j)
cout << "j = " << j << " p = "
<< static_cast<double>(outcomes[j])/trials
<< endl;
}
This is replaced by
//The following program computes
//the probability for dice possibilities
#include <iostream>
#include <random>
#include <ctime>
using namespace std;
const int sides = 6;
int main(void)
{
const int n_dice = 2;
uniform_int_distribution<unsigned> u(1,6);
default_random_engine e(time(0));
cout << "\nEnter number of trials: ";
int trials;
cin >> trials; //compare to scanf
int* outcomes = new int[n_dice * sides +1];
for (int j = 0; j < trials; ++j) {
int roll = 0;
for (int k = 1; k <= n_dice; ++k) {
roll += u(e);
}
outcomes[roll]++;
}
cout << "probability\n";
for (int j = 2; j < n_dice * sides + 1; ++j)
cout << "j = " << j << " p = "
<< static_cast<double>(outcomes[j])/trials
<< endl;
}
The library <random> has modern random number generator
including a default random engine declaration as seen in this
example. Popular engines included are
