#include <iostream> #include <cmath> class Circle { private: double radius; public: // Constructor Circle(double r) { radius = r; } // Mutator to set the radius void setRadius(double r) { radius = r; } // Accessor to get the radius double getRadius() const { return radius; } // Compute area double area() const { return M_PI * pow(radius, 2); } // Compute diameter double diameter() const { return 2 * radius; } // Compute circumference double circumference() const { return 2 * M_PI * radius; } }; int main() { double radius1, radius2; cout<<"Please input radius1:"<<endl; cin>>radius1; cout<<"Please input radius2:"<<endl; cin>>radius2; Circle c1(radius1); Circle c2(radius2); std::cout << "Circle 1: radius=" << c1.getRadius() << ", area=" << c1.area() << ", diameter=" << c1.diameter() << ", circumference=" << c1.circumference() << std::endl; c1.set_radius(radius1); c2.set_radius(radius2); std::cout << "Circle 2: radius=" << c2.getRadius() << ", area=" << c2.area() << ", diameter=" << c2.diameter() << ", circumference=" << c2.circumference() << std::endl; return 0; }为什么运行不出来

这段代码存在几个问题：

1.在类中定义了一个构造函数，但在主函数中没有使用这个构造函数来创建对象，而是直接使用了默认构造函数，应该改为使用构造函数来创建对象。

2.在类中定义了一个名为setRadius()的函数，但在主函数中却使用了一个名为set_radius()的函数，应该将其改为setRadius()。

以下是修改后的代码：

#include <iostream> 
#include <cmath>  

class Circle { 
private:     
    double radius; 
public:     
    // Constructor     
    Circle(double r) {         
        radius = r;     
    }      
    // Mutator to set the radius     
    void setRadius(double r) {         
        radius = r;     
    }      
    // Accessor to get the radius     
    double getRadius() const {         
        return radius;     
    }      
    // Compute area     
    double area() const {         
        return M_PI * pow(radius, 2);     
    }      
    // Compute diameter     
    double diameter() const {         
        return 2 * radius;     
    }      
    // Compute circumference     
    double circumference() const {         
        return 2 * M_PI * radius;     
    } 
};  

int main() {          
    double radius1, radius2; 	 
    std::cout<<"Please input radius1:"<<std::endl;      
    std::cin>>radius1;      
    std::cout<<"Please input radius2:"<<std::endl;      
    std::cin>>radius2;      
    Circle c1(radius1); 	 
    Circle c2(radius2);     
    std::cout << "Circle 1: radius=" << c1.getRadius()               
              << ", area=" << c1.area()               
              << ", diameter=" << c1.diameter()               
              << ", circumference=" << c1.circumference() << std::endl;     
    c1.setRadius(radius1);     
    c2.setRadius(radius2);     
    std::cout << "Circle 2: radius=" << c2.getRadius()               
              << ", area=" << c2.area()               
              << ", diameter=" << c2.diameter()               
              << ", circumference=" << c2.circumference() << std::endl;         
    
    return 0; 
}

运行这段代码时，先输入radius1和radius2，然后程序会输出两个圆的半径、面积、直径和周长。