按引用传递参数

#include <iostream>
using namespace std;

const double pi = 3.14159;
//double Area(double radius)
//{
// double result = 0;
// return result = pi * radius * radius;
//}
//
//int main()
//{
// double ra = 0;
// cin >> ra;
//
// double app = 0;
// app= Area(ra);
// cout << app << endl;
// return 0;
//}//---------------------------------------------------下面使用按引用传递参数

void Area(double radius, double& result)
{
result= pi * radius * radius;
}

int main()
{
double radius = 0;
cin >> radius;

double app = 0;
Area(radius, app);
cout << app << endl;
return 0;
}