c++例題 構造函數（一）

 【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。請用上類似的構造函數，自己設計main()函數，對設計的類進行測試。

[cpp]
#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; 
} 

#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;
}