#include <iostream>
#include <sstream>
 
using namespace std;
 
// Widget.h:
class Widget {
private:
    string name;
 
    // We want the serial number to be constant for each widget, but we each should get its own value.
    // We will mark the serial number as constant but not give it a value yet, which seems a little strange.
    // Remember that the .h is just a template, nothing is really being created.
    const int serialNumber;
    // In this context static means that there is only one nextSerialNumber value, not one for each object.
    // All instance of the class can see and set this value, but they all see the same value. In other
    // languages this is called a "Class variable" indicating that it is shared by all instances of the
    // class.
    static int nextSerialNumber;
public:
    Widget(string);
    string ToString();
 
    int PeekAtNextSerialNumber();
};
 
// Widget.cpp
 
// The next line has two interesting features:
//  1) When we create a new widget we can use initialization to give it a value for the constant serialnumber!
//     This is allowed because when the constructor is executed, a new widget is coming into existence and
//     needs to know what value it's constant should have.
//  2) As noted above, there is only one variable called nextSerialNumber, we can use that to set the new
//     widget's serial number and then add one, in preparation for the next widget to be created.
Widget::Widget(string aName) : name(aName), serialNumber(nextSerialNumber++){
}
 
string Widget::ToString() {
    ostringstream tempstream("");
 
    tempstream << "Name: \"" << name << "\"\tSerial Number: " << serialNumber;
    return tempstream.str();
 
}
 
// This method is hear ONLY for educational or debugging purposes, generally you would not have such a method.
int Widget::PeekAtNextSerialNumber() {
    return nextSerialNumber;
}
 
// We need to set the first serial number, like methods identified in the .h but not defined until in the .cpp
// we can do that with variables too.
int Widget::nextSerialNumber = 0;
 
// end of what would be in Widget.cpp
 
int main() {
    cout << "Create wheelWidget." << endl;
    Widget wheelWidget("A Wheel");
 
    cout << "wheelWidget contents: " << wheelWidget.ToString() << endl;
    cout << endl;
    cout << "AFTER having created the wheelWidget the value of nextSerialNumber is : " << wheelWidget.PeekAtNextSerialNumber() << endl;
    cout << endl << endl;
 
    cout << "Create leverWidget." << endl;
    Widget leverWidget("A Lever");
 
    cout << "leverWidget contents: " << leverWidget.ToString() << endl;
    cout << endl;
    cout << "AFTER having created the leverWidget the value of nextSerialNumber is : " << leverWidget.PeekAtNextSerialNumber() << endl;
    cout << "Because nextSerialNumber is shared by all instance of Widget, wheelWidget also sees the value of nextSerialNumber as: " << wheelWidget.PeekAtNextSerialNumber() << endl;
    cout << endl << endl;
 
    cout << "Create rampWidget." << endl;
    Widget rampWidget("A Ramp");
 
    cout << "rampWidget contents: " << rampWidget.ToString() << endl;
    cout << endl;
    cout << "AFTER having created the rampWidget the value of nextSerialNumber is : " << rampWidget.PeekAtNextSerialNumber() << endl;
    cout << "Because nextSerialNumber is shared by all instance of Widget, leverWidget also sees the value of nextSerialNumber as: " << leverWidget.PeekAtNextSerialNumber() << endl;
    cout << "Because nextSerialNumber is shared by all instance of Widget, wheelWidget also sees the value of nextSerialNumber as: " << wheelWidget.PeekAtNextSerialNumber() << endl;
 
 
 
 
    //system("pause");
 
    return 0;
}

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