PC World Komputer 1997 May/Pcwk0597.iso/borland/cb/setup/cbuilder/data.z/ICECREAM.CPP

C/C++ Source or Header | 1997-02-28 | 5KB | 196 lines

/**************************************************************************
 *
 * icecream.cpp - priority queue example program. Section 11.3.1
 *
 * $Id: icecream.cpp,v 1.5 1995/08/29 19:01:39 oberg Exp $
 *
 * $$RW_INSERT_HEADER "slyrs.cpp"
 *
 **************************************************************************/

# include <vector>
# include <queue>

# include <iostream.h>
using namespace std;

//
//    class event
//    execution event in a descrete event driven simulation
//

class event {
public:
    // construct sets time of event
    event (unsigned int t) : time(t) { };

    // time is a public data field
    const unsigned int time;

    // execute event my invoking this method
    virtual void processEvent() = 0;
};

inline void destroy(event **) {}

struct eventComparison {
    bool operator () (event * left, event * right)
        { return left->time > right->time; }
};

//
//    class simulation
//        framework for discrete event-driven simulations
//    written by Tim Budd, for Rogue Wave, 1995
//

class simulation {
public:
        // constructor
    simulation () : eventQueue(), time(0) {}

        // start and run simulation
    void run ();

        // return current time
    unsigned int time;

        // schedule a future event
    void  scheduleEvent (event * newEvent)
        { eventQueue.push(newEvent); }

protected:
    priority_queue<event*, vector<event *>, eventComparison> eventQueue;
};

void simulation::run()
{
    while (! eventQueue.empty()) {
        event * nextEvent = eventQueue.top();
        eventQueue.pop();
        time = nextEvent->time;
        nextEvent->processEvent();
        delete nextEvent;
        }
}

//
//    ice cream store simulation
//

class storeSimulation : public simulation {
public:
    storeSimulation()
        : freeChairs(35), profit(0.0), simulation() { }

    bool canSeat(unsigned int numberOfPeople);
    void order(unsigned int numberOfScoops);
    void leave(unsigned int numberOfPeople);

        // data fields
    unsigned int freeChairs;
    double profit;
} theSimulation;

class arriveEvent : public event {
public:
    arriveEvent (unsigned int time, unsigned int groupSize)
        : event(time), size(groupSize) { }
    virtual void processEvent();
private:
    unsigned int size;
};

class orderEvent : public event {
public:
    orderEvent (unsigned int time, unsigned int groupSize)
        : event(time), size(groupSize) { }
    virtual void processEvent();
private:
    unsigned int size;
};

class leaveEvent : public event {
public:
    leaveEvent (unsigned int time, unsigned int groupSize)
        : event(time), size(groupSize) { }
    virtual void processEvent();
private:
    unsigned int size;
};

int irand(int n)
    // return random integer between 0 and n
{ return (rand()/10) % n; }

void arriveEvent::processEvent()
{
    if (theSimulation.canSeat(size))
        theSimulation.scheduleEvent(new orderEvent(time + 1 + irand(4), size));
}

void orderEvent::processEvent()
{
        // each person orders some number of scoops
    for (int i = 0; i < size; i++)
        theSimulation.order(1 + irand(4));
        // then we schedule the leave event
    theSimulation.scheduleEvent(new leaveEvent(time + 1 + irand(10), size));
}

void leaveEvent::processEvent()
{
    theSimulation.leave(size);
}

bool storeSimulation::canSeat(unsigned int numberOfPeople)
    // if sufficient room then seat customers
{
    cout << "Time: " << time;
    cout << " group of " << numberOfPeople << " customers arrives";
    if (numberOfPeople < freeChairs) {
        cout << " is seated" << endl;
        freeChairs -= numberOfPeople;
        return true;
        }
    else {
        cout << " no room, they leave" << endl;
        return false;
        }
}

void storeSimulation::order(unsigned int numberOfScoops)
    // service icecream, compute profits
{
    cout << "Time: " << time;
    cout << " serviced order for " << numberOfScoops << endl;
    profit += 0.35 * numberOfScoops;
}

void storeSimulation::leave(unsigned int numberOfPeople)
    // people leave, free up chairs
{
    cout << "Time: " << time;
    cout << " group of size " << numberOfPeople << " leaves" << endl;
    freeChairs += numberOfPeople;
}

int main() {
    cout << "Ice Cream Store simulation from Chapter 9"  << endl;
        // load queue with some number of initial events
    unsigned int t = 0;
    while (t < 20) {
        t += irand(6);
        cout << "pumping queue with event " << t << endl;
        theSimulation.scheduleEvent(new arriveEvent(t, 1 + irand(4)));
        }

        // run the simulation
    theSimulation.run();
    cout << "Total profits " << theSimulation.profit << endl;

    cout << "End of ice cream store simulation" << endl;
    return 0;
}