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Question

构造一个圆类Circle属性为半径radius圆周长和面积，实现根本输入的半径计算周长和面积并输出。要求定义以半径为参数，缺省值为零的构造函数，且周长和面积的计算在构造函数中实现

Answer 1

#define _USE_MATH_DEFINES
#include <iostream>
#include <cmath>
#include <stdexcept>

class Circle
{
public:
    Circle(double radius = 0.0) : _radius(radius), _circumference(2.0 * M_PI * _radius), _area(M_PI * _radius * _radius)
    {
        if (radius < 0.0)
            throw std::invalid_argument("invalid radius");
    }

    double radius() const { return _radius; }
    double circumference() const { return _circumference; }
    double area() const { return _area; }

private:
    double _radius;
    double _circumference;
    double _area;
};

int main()
{
    try
    {
        double radius;
        std::cout << "请输入半径: ";
        std::cin >> radius;
        Circle circle(radius);
        std::cout << "周长: " << circle.circumference() << '\n';
        std::cout << "面积: " << circle.area() << '\n';
    }
    catch (const std::exception &e)
    {
        std::cerr << e.what() << std::endl;
    }
    return 0;
}