自定义圆类

vs2015编译运行

#include<iostream>
using namespace std;
class circle {
private:  //私有成员类内可见
    const double PI = 3.1415926; //C++11新标准类，类内成员直接初始化
    double r = 1.0;
public:
    circle() = default;       //C++11新标准类，使编译器生成合成默认构造函数
    circle(double R):r(R){}
    void setr(double R);  //设定半径
    double Getr();        //获取半径
    double GetArea();     //获取面积
    double GetGirth();    //获取周长
};
void circle::setr(double R)
{
    r = R;
}
double circle::Getr(){
    return r;
}
double circle::GetArea(){
    return PI*r*r; 
}
double circle::GetGirth() {
    return 2 * PI*r;
}
int main() {
    circle c1;  //调用默认构造函数
    cout <<"半径："<<c1.Getr() << endl;
    cout << "面积：" << c1.GetArea() << endl;
    cout << "周长：" << c1.GetGirth() << endl;
    system("pause");
}