#include <iostream>
#include <ostream>
#include <string>
#include <time.h>

using namespace std; // allows unqualified use of identifiers of namespace std

class Singleton
{
    private:
    /* Here will be the instance stored. */
    static Singleton* instance;

    /* Private constructor to prevent instancing. */
    Singleton();

    int max;
    int factor;
    int increment;
    unsigned long int actualrandom;

    public:
    /* Static access method. */
    static Singleton* getInstance();

    bool ask_yn(const char * msg);

    void random_number();

    void random_seed();
};

/* Null, because instance will be initialized on demand. */
Singleton* Singleton::instance = 0;

Singleton* Singleton::getInstance()
{
    if (instance == 0)
    {
        instance = new Singleton();
    }

    return instance;
}

Singleton::Singleton(){
    this->max=1000;
    this->factor=623;
    this->increment=525;
    this->actualrandom=((this->factor*157)+this->increment)%this->max;
}


bool Singleton::ask_yn(const char * msg) {
    cout << msg << " (y/n)? " << flush;
    char answer;
    cin >> answer;
    if (answer == 'y' || answer == 'Y')
        return true;
    else return false;
    }

void Singleton::random_number() {
    this->actualrandom = ((this->factor * this->actualrandom) + this->increment) % this->max;
    cout<<this->actualrandom<<"\n";
}

void Singleton::random_seed(){
    time_t timer;
    time(&timer);
    // timer*100 gives negative number
    this->actualrandom= timer%this->max;
}

int main(){
    //new Singleton(); // Won't work
    Singleton* s = Singleton::getInstance(); // Ok

    if(s->ask_yn("Random seed the generator")==true){
        s->random_seed();
    }

    do{
        s->random_number();
    }while(s->ask_yn("Another random number?"));

}