例9.4 將例9.3程序中的構(gòu)造函數(shù)改用含默認(rèn)值的參數(shù)，長、寬、高的默認(rèn)值均為10。
在例9.3程序的基礎(chǔ)上改寫如下： 
#include <iostream>
using namespace std;
class Box
{public:
Box(int h=10,int w=10,int len=10);        //在聲明構(gòu)造函數(shù)時(shí)指定默認(rèn)參數(shù)
int volume( );
 private:
int height;
int width;
int length;
};
Box∷Box(int h,int w,int len)        //在定義函數(shù)時(shí)可以不指定默認(rèn)參數(shù)
{height=h;
width=w;
length=len;
}

int Box∷volume( )
{return(height*width*length);
}

int main( )
{
Box box1;                   //沒有給實(shí)參 
cout<<″The volume of box1 is ″<<box1.volume( )<<endl;
Box box2(15);               //只給定一個(gè)實(shí)參
cout<<″The volume of box2 is ″<<box2.volume( )<<endl;
Box box3(15,30);            //只給定2個(gè)實(shí)參
cout<<″The volume of box3 is ″<<box3.volume( )<<endl;
Box box4(15,30,20);            //給定3個(gè)實(shí)參
cout<<″The volume of box4 is ″<<box4.volume( )<<endl;
return 0;
}