Distributions.cpp

#include<iostream>
#include<string>
#include<random>
#include<vector>
#include<sstream>
#include<chrono>

using namespace std;

int main(){
    unsigned int seed = chrono::steady_clock::now().time_since_epoch().count();
    default_random_engine e(seed);
    //The range of the generated number is between [e.min(), e.max()]
    cout << e() << endl; 

    //If we want to generate a random number from the range [0, 5]
    cout << e() % 6 << endl;
    // Issues with the above code:
    /* 1. Bad quality of randomness. The default engine can produce the 
    *  random number pretty good between [e.min(), e.max()]. With % 
    *  operation, this randomness does not holds.
    *  2. Can only provide a uniform distribution! 
    */

    //Uniform distribution between [0, 5], inclusive
    uniform_int_distribution<int> distr(0, 5);
    //Now the random engine provides the randomness and distribution 
    //object provides the distribution!
    cout << distr(e) << endl; 

    //Here Range is [0, 5), 5 not included
    uniform_real_distribution<float> distrR(0, 5);
    cout << distrR(e) << endl; 

    //We can easily generate other distributions.
    //poisson distribution
    poisson_distribution<int> distrP(1.0); // 1.0 is the mean
    cout << distrP(e) << endl; 

    cout << "Normal distribution: " << endl;
    //10.0 is mean, 3.0 is standard deviation
    normal_distribution<double> distrN(10.0, 3.0);
    vector<int> v(20);
    for(int i = 0; i < 800; i++){
        int num = distrN(e); //convert double to int!
        if(num >= 0 && num < 20){
            v[num]++; //v[num] represents the frequency of num
        }
    }
    //Try to run the code, and you can see the distribution 
    //yourself!
    for(int i = 0; i < 20; i++){
        cout <<"  " << std::string(v[i], '+') << endl;
    }
    cout << endl;

    system("pause");
    return 0;
}