3.22

#include<iostream>
using namespace std;
class Circle
{
    private:
		double radius;
		double cs;
	public:
		void area()
		{
        	cs=3.14*radius*radius;
        	cout<<"圆的面积为："<<cs<<endl;
		}
		void radius_input()
		{
        	cout<<"请输入圆的半径："<<endl;
			cin>>radius;
		}
};
int main()
{
	Circle circle1;
    circle1.radius_input();
    circle1.area();
	return 0;
}