3-4 计算长方形的周长和面积
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 len;
double wid;
public:
Rect(double x=0,double y=0);
Rect(const Rect &b);
const void display()
{
cout << "the length and width of r1 is:" << len << ","<< wid << endl;
cout << "the perimeter of r1 is:" << (len + wid) * 2<<endl;
cout << "the area of r1 is:" << len * wid << endl;
}
const void display1()
{
cout << "the length and width of r2 is:" << len << ',' << wid<< endl;
cout << "the perimeter of r2 is:" << (len + wid) * 2 << endl;
cout << "the area of r2 is:" << len * wid << endl;
}
};
Rect::Rect(double x,double y)
{
len=x;
wid=y;
}
Rect::Rect(const Rect &b)
{
len=b.len;
wid=b.wid;
}
int main()
{
double x,y;
cin>>x>>y;
if(x<0||y<0)
{
x=0;
y=0;
}
Rect rect(x,y);
Rect rect1=rect;
rect.display();
rect1.display1();
return 0;
}
原文：http://www.cnblogs.com/clnchanpin/p/7275255.html