c++例题 构造函数（一）

题目来自：http://blog.csdn.net/sxhelijian/article/details/8723847

【项目1拓展（选做）】请自行设计一个矩形类，可以计算矩形的面积、周长、对象线，判断是否是正方形。请用上类似的构造函数，自己设计main()函数，对设计的类进行测试。

#include <iostream>#include <cmath>using namespace std;class Rectangle{private:double length;double width;public:Rectangle():length(1),width(1){}Rectangle(double len,double wid):length(len),width(wid){}//   Rectangle(double len=1,double wid =1):length(len),width(wid){}double area(void);double perimeter(void){ return 2*(length+width); }double diagonal(void) { return sqrt(length*length+width*width); }bool square_or_not(void) { return length==width?true:false; }    void show_message(void);};//Rectangle::Rectangle(double len,double wid){length = len;width = wid;}double Rectangle::area(void){return length*width;}void Rectangle::show_message(void){cout << "矩形的长宽分别为: " << length << '\t' << width <<endl;cout << "周长: " << perimeter() << "面积: " << area() << "对角线长度: "<< diagonal() << endl;cout << "是否为正方形? " << square_or_not() << endl;}int main(){Rectangle rect1;rect1.show_message();Rectangle rect2(3,4);rect2.show_message();return 0;}