对象的复制（复制构造函数）

# include <iostream>
# include <string>
using namespace std;
class rect
{
private:
    double length;
    double width;
public:
    rect(double length=0,double width=0);
    //rect(const rect&); //对象复制构造函可有可无
    void output()
    {
        if(length<=0 || width<=0)
            cout<<"0,0"<<endl;
        else
        cout<<length<<','<<width<<endl;
    }
    void calculate1()
    {
            if(length<=0 || width<=0)
                cout<<'0'<<endl;
            else
        cout<<2*(length+width)<<endl;
    }
    void calculate2()
    {
            if(length<=0 || width<=0)
                cout<<'0'<<endl;
            else
        cout<<length*width<<endl;
    }
    void input()
    {
        cin>>length>>width;
    }

};
rect::rect(double h,double w)
{
    length=h;
    width=w;
}
//rect::rect(const rect&b)
//{
//    length=b.length;
//    width=b.width;
//}
int main()
{
    rect r1(3.0,2.0);
    r1.input(); //注意调用成员函数的括号必须得写
    cout<<"the length and width of r1 is:";
    r1.output();
    cout<<"the perimeter of r1 is:";
    r1.calculate1();
    cout<<"the area of r1 is:";
    r1.calculate2();
    rect r2(r1);//对象的复制。
    cout<<"the length and width of r2 is:";
    r2.output();
    cout<<"the perimeter of r2 is:";
    r2.calculate1();
    cout<<"the area of r2 is:";
    r2.calculate2();
    return 0;
}