求大神给我个例子,怎么把下面这个简单程序换成两个或三个文件来执行
#include<iostream>
using namespace std;
class circle
{
private:
double radius;
public:
void input();
void get_radius();
void output();
};
void circle::get_radius()
{
double r;
cin >> r;
radius = r;
}
void circle::output()
{
cout << "您所求的圆的半径是:" << radius*radius*3.14 << endl;
}
int main()
{
void get_radius(double r);
void get_area();
void output();
circle c;
c.get_radius();
c.output();
}