#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

//struct 
struct Circle
{
	double radius;
	double girth;
	double area;
};
//function(struct variable） 
double myGirth(struct Circle c1)
{
	double r1 = c1.radius;
	return 2*3.14149*r1;
}
//function(struct variable）
double myRadius(struct Circle * c1)
{
	c1->radius = 10.5;
	return c1->radius;
}

//function(struct variable）
double setArea(struct Circle * c1)
{
	double r1 = c1->radius;
	c1->area = 3.14149*r1*r1; 
	return c1->area;
}

//function(struct variable）
void setData(struct Circle * c1, double r1)
{
	c1->radius = r1;
	c1->girth = 2*3.14149*r1;
	c1->area = 3.14149*r1*r1;
}
//......................
int main(int argc, char** argv) {
	//1.
	struct Circle cir1;
	cir1.radius = 2.5;
	cir1.area = myGirth(cir1);
	cout<<"r = "<<cir1.radius<<", area = "<<cir1.area<<endl;
	
	//2.函數的參數，若用一般結構變數==>這個只是local變數，修改後回到main()，該筆數就消失了
	cout<<endl; 
	cout<<"（before）r = "<<cir1.radius<<endl;
	myRadius(&cir1);
	cout<<"（after）r = "<<cir1.radius<<endl;
	
	//結論1：函數傳遞參數 ==> 一般結構變數 ==> local變數 ==> 被修改值，回到main()無效 
	//結論1：函數傳遞參數 ==>若要保存被修改結構變數值：兩個方法：
	//（1）傳遞參數：參考 結構變數 
	//（2）傳遞參數：指標 結構變數
	
	//3.指標 結構變數
	cout<<endl;
	cout<<"r = "<<cir1.radius<<", area = "<<setArea(&cir1)<<endl;
	cout<<"r = "<<cir1.radius<<", area = "<<cir1.area<<endl;
	
	//4.指標 結構變數：方法1：
	struct Circle cir2;
	setData(&cir2, 10.5);
	cout<<endl;
	cout<<"r = "<<cir2.radius<<", area = "<<cir2.area<<", girth = "<<cir2.girth<<endl;
	 
	//5.指標 結構變數：方法2：
	struct Circle * cir3 = new struct Circle;
	setData(cir3, 10.5);
	cout<<endl;
	cout<<"r = "<<cir3->radius<<", area = "<<cir3->area<<", girth = "<<cir3->girth<<endl;
	
	
	
	return 0;
}