c++例題 建構函式（一）

題目來自：http://blog.csdn.net/sxhelijian/article/details/8723847

【項目1拓展（選做）】請自行設計一個矩形類，可以計算矩形的面積、周長、對象線，判斷是否是正方形。請用上類似的建構函式，自己設計main()函數，對設計的類進行測試。

#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 << "矩形的長寬分別為: " << length << '\t' << width <<endl;cout << "周長: " << perimeter() << "面積: " << area() << "對角線長度: "<< diagonal() << endl;cout << "是否為正方形? " << square_or_not() << endl;}int main(){Rectangle rect1;rect1.show_message();Rectangle rect2(3,4);rect2.show_message();return 0;}