声明一个Circle类，有：数据成员Radius(半径)，成员函数GetArea()计算圆的面积，构造函数Circle(float radius)进行初始化和析构函数。在主函数中创建一个Circle类的对象进行测试（输入一个数值，作为Circle类对象的半径，调用该对象的GetArea()求以该数值为半径的圆的面积）-Declare a Circle class, are: data members Radius (radius) member function GetArea () to calculate the area of ​ ​ a circle, the constructor Circle (float radius) to initialize and destructors. Creating a Circle class of objects in the main function tests (enter a value, as the radius Circle class object, call the object' s GetArea () request to the value of the radius of the circle area)