3.22声明一个circle类。数据成员radius和数据函数area（）。
#include<iostream>using namespace std;class cired{public:cired (int r){radius=r;}void area(){int x=3*radius*radius;cout<<"半径为"<<radius<<"的圆的面积是"<<x<<endl;}private:int radius;};int main(){cired c1(5);c1.area();cired c2(7);c2.area();return 0;}3.23建立类cylinder，，数据成员有半径和高，成员函数vol（）。
#include<iostream>using namespace std;class cylincler{public:cylincler (double r,double h);void vol(){double v;v=3.14*radius*radius*high;cout<<"半径为"<<radius<<"，"<<"高为"<<high<<"的圆柱体的体积为"<<v<<endl;}private:double radius;double high;};cylincler ::cylincler(double r,double h){radius=r;high=h;}int main(){cylincler c1(23,11);c1.vol();cylincler c2(2,4);c2.vol();return 0;}2.24定义一个日期类date，该类的对象存放一个日期。
#include<iostream>using namespace std;class date{public:void setdate(int y=2015,int m=3,int d=29);void printdate();void getyear();void getmonth();void getday(); date(const date& p) {year=p.year;month=p.month;day=p.day;cout<<"using copy constructor"<<endl; } date()//没有默认的适当的构造函数 {}private:int year;int month;int day;};void date::setdate(int y,int m,int d){year=y;month=m;day=d;}void date::printdate(){cout<<"日期是："<<year<<"."<<month<<"."<<day<<"."<<endl;}void date::getyear(){cout<<"该日期的年份是"<<year<<endl;}void date::getmonth(){cout<<"该日期的月份是"<<month<<endl;}void date::getday(){cout<<"该日期的在"<<day<<"号"<<endl;}int main(){date d2,d1;d1.setdate(2014,11,3);d1.printdate();d2.setdate();d2.getyear();date c3(d1);c3.getmonth();date c4=d2;c4.getday();return 0;}
如果有可能，我带你去远行。躺在德德玛的草原，
