定义一个矩形类CRect，有长length和宽width两个属性，有成员函数
构造函数1：对值初始化，并输出“有参数的构造函数被调用”
构造函数2：没有参数，输出“无参数的构造函数被调用”
析构函数：输出“析构函数被调用”
SetLength(int x):设置长度
SetWidth(int x):设置宽度
GetArea():计算矩形面积,并输出计算结果(Define a rectangle class CRect with two attributes, a long length and a wide width, with a member function

Constructor 1: initialization of the value, and output the "parameter constructor is called"

Constructor 2: there is no parameter, and the output "no parameter constructor is called"

Destructor: output "destructor is called"

SetLength (int x): setting the length

SetWidth (int x): setting the width

GetArea (): calculate the rectangle area and output the calculation result)