创建函数并访问

class Circle{public:    double radius;    Circle() {                             //Constructors:        radius = 1;                        //Initialize objects(构造函数：初始化对象)    }                                      //Has the same name as the defining class(与类同名)                                           //No return value(无返回值)    Circle(double newRadius) {             //constructors can be overloaded(可重载)        radius = newRadius;                //may be no arguments(可不带参数)    }    double getArea() {                             return radius * radius *3.14159;    }};

A class may be declared without constructors(类里面也可以不声明构造函数)

• A no-arg constructor with an empty body is implicitly declared in the class.
  (编译器会提供一个带有空函数体的无参构造函数)

• This constructor,called a default constructor is provided automatically **only if no
  constructors are explicitly declared in the class**.
  (只有当未明确声明构造函数时，编译器不会提供这个构造函数，并称之为“默认构造函数”)

【Constructing Objects(创建对象)】
Without Arguments;(无参数)
ClassName objectName;
For example;
Circle circle1;// the no-arg constructor
// is invoked

With Arguments;
ClassName objectName(arguments);
For example:
Circle circle2(5.5);