#include <iostream>
using namespace std;

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

//object class: Circle
class Circle
{
public:
	int radius;
	void showGirth()
	{
		cout<<"圓周長 = "<<2*3.14159*radius<<endl;
	}
	void showArea()
	{
		cout<<"面積 = "<<3.14159*radius*radius<<endl;
	}	
};
//宣告函數
int & show1(); 
Circle & setCir(Circle & c, int r);
 
int main(int argc, char** argv) {
	//1.函數的return值是參考變數
	//用途：經常用在物件變數object
	
	//2.函數的return值是一般參考變數
	int k = 10;
	int & a = k;
	cout<<"a = "<<a<<endl;
	a = show1();
	cout<<"a = "<<a<<endl;
	
	//3.物件變數object
	cout<<endl;

	Circle c;
	c.radius = 3;
	c.showGirth();
	c.showArea();
	
	cout<<endl;
	c.radius = 5;
	c.showGirth();
	c.showArea();
	
	//4.函數的return值是參考物件變數object
	//目的：把上方的兩階段設定半徑+印出面積 ===> 濃縮成一行指令（先設定半徑，然後印出面積） 
	cout<<endl;
	setCir(c, 3).showGirth();
	setCir(c, 3).showArea();
	//原理： setCir(c, 3)設定半徑後，會傳回Circle物件 ==> Circle物件.showArea() 
	
	
	return 0;
}

//function 1 : show1()
int & show1()
{
	int n = 100;
	return n;
} 

//function 2: setCir(...)
Circle & setCir(Circle & c, int r)
{
	c.radius = r;
	return c;
}