main.cpp

C++ Source code from a tutorial

#include <iostream>
#include <stdlib.h>
#include <string>

using namespace std;

class Observer;
class Subject {
    friend Observer;
protected:
    int Count;
    Observer *List[100];
    void AddObserver(Observer *Item);
    void RemoveObserver(Observer *Item);
public:
    Subject() { Count = 0; }
    void Event();
};

class Observer {
protected:
    Subject *subj;
public:
    virtual void Respond() = 0;
    Observer(Subject *asubj) { 
        subj = asubj;
        subj->AddObserver(this);
    }
    ~Observer() { subj->RemoveObserver(this); }
};

class Dog : public Observer {
public:
    void Respond();
    Dog(Subject *asubj) : Observer(asubj) {}
};

class Police : public Observer {
protected:
    string name;
public:
    Police(Subject *asubj, string myname) : Observer(asubj) { name = myname; }
    void Respond();
};

void Dog::Respond() {
    cout << "Bark bark" << endl;
}

void Police::Respond() {
    cout << name << ": 'Drop the weapon! Now!'" << endl;
}


void Subject::AddObserver(Observer *Item) {
    List[Count] = Item;
    Count++;
}

void Subject::RemoveObserver(Observer *Item) {
    int i;
    bool found = false;
    for (i=0; i < Count; i++) {
        if (found) {
        }
        else if (List[i] == Item) {
            found = true;
            List[i] = List[i+1];
        }
    }
    if (found) {
        Count--;
    }
}

void Subject::Event() {
    int i;
    for (i=0; i < Count; i++) {
        List[i]->Respond();
    }
}

int main(int argc, char *argv[])
{
    Subject Alarm;

    Dog *Fido = new Dog(&Alarm);
    Police *TJHooker = new Police(&Alarm, "TJ");
    Police *JoeFriday = new Police(&Alarm, "Joe");
    
    cout << "TJ on the beat" << endl;
    Alarm.Event();
    cout << endl;

    cout << "TJ off for the day" << endl;
    delete TJHooker;
    Alarm.Event();
    
    system("PAUSE");	
    return 0;
}