3.22

#include<iostream>using namespace std;const double p=3.14;class circle{public:circle(double r1);double area(){ return p*r*r;}void show();private:double r;};circle::circle(double r1){r=r1;};void circle::show(){cout<<"圆形的半径为"<<r<<endl     <<"圆的面积为"<<area()<<endl;}int main(){circle c1(4);c1.show();return 0;}