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;
}