作业3.22

#include<iostream> using namespace std; class circle{public:float area();        circle();         circle(float r);public:float radius;};circle::circle(){    radius=1.0;}circle::circle(float r){    radius=r;}float circle::area(){ return radius*radius*3.14;}void main() {    circle c1;   cout<<"圆1的面积="<<c1.area()<<endl;circle c2(5);cout<<"圆2的面积="<<c2.area()<<endl;}