类中有私有数据成员Length(长)、Width(宽)。由具有缺省參数值的构造函数对其初始化，函数原型为：Rect(double Length=0, double Width=0); 再为其定义拷贝构造函数，形參为对象的常引用。函数原型为：Rect(const Rect &); 编写主函数。创建Rect对象r1初始化为长、宽数据，利用r1初始化还有一个Rect对象r2。分别输出对象的长和宽、周长和面积。
输入两个实数，中间用一个空格间隔；代表长方形的长和宽
共同拥有6行；
分别输出r1的长和宽。r1的周长；r1的面积；r2的长和宽；r2的周长；r2的面积。注意单词与单词之间用一个空格间隔
56 32
the length and width of r1 is:56,32 the perimeter of r1 is:176 the area of r1 is:1792 the length and width of r2 is:56,32 the perimeter of r2 is:176 the area of r2 is:1792
输入-7.0 -8.0
输出
the length and width of r1 is:0,0
the perimeter of r1 is:0
the area of r1 is:0
the length and width of r2 is:0,0
the perimeter of r2 is:0
the area of r2 is:0
#include <iostream>
using namespace std;
class Rect
{
private:
double l;
double w;
public:
Rect (double x=0,double y=0);
Rect (const Rect &a);
const void display1()
{
cout<<"the length and width of r1 is:"<<l<<","<<w<<endl;
cout<<"the perimeter of r1 is:"<<(l+w)*2<<endl;
cout<<"the area of r1 is:"<<l*w<<endl;
}
const void display2()
{
cout<<"the length and width of r2 is:"<<l<<","<<w<<endl;
cout<<"the perimeter of r2 is:"<<(l+w)*2<<endl;
cout<<"the area of r2 is:"<<l*w<<endl;
}
};
Rect::Rect(double x,double y)
{
l=x;
w=y;
}
Rect::Rect(const Rect & a)
{
l=a.l;
w=a.w;
}
int main()
{
double x,y;
cin>>x>>y;
if(x<0|| y<0)
{
x=0;
y=0;
}
Rect rect(x,y);
Rect rect_copy=rect;
rect.display1();
rect_copy.display2();
return 0;
}
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原文：http://www.cnblogs.com/mengfanrong/p/4744216.html