Question

C++的一道程序填空题，请高手帮忙看看·······

#include<iostream.h>
class Time
{ public:
Time(int h, int m) {hours=h; minutes=m;}
________(9)________ Time12();
________(10)________ Time24(Time time);
private: int hours, minutes;
};
_________(11)__________ Time12()
{ if(hours>12) { cout<<hours-12<<":"<<minutes<<"PM\n" ; }
else cout<<hours<<":"<<minutes<<"AM\n" ;
}
void Time24(Time time)
{ cout _____________(12)_______________ ;}
void main()
{ Time T1(20,30), T2(10,45);
T1.Time12(); Time24(T1); T2.Time12(); Time24(T2);
}
输出： 8:30PM
20:30
10:45AM
10:45

Answer 1

考察的主要是虚函数和友元函数；
virtual一般可以省，但这道题不可以省，上机给你调试好的，字也是手打的，给点辛苦钱呗；

友元：友元是一种定义在类外部的普通函数，它需要在类体内进行说明，在说明时，前面加上 friend 。友元不是成员函数，但可以访问类的私有成员。目的在于提高函数的运行效率。但是设置友元是以破坏封装性为代价的。

9.virtual void
10. friend void
11.void Time::
12.<<time.hours<<":"<<time.minutes<<endl;

Answer 2

9-void
10-friend void
11-void time::
12-<<time.hours<<":"<<time.minutes<<endl

Answer 3

#include<iostream>
using namespace std;
class Time
{
public:
Time(int h, int m) {hours=h; minutes=m;}
void Time12();
friend void Time24(Time time);
private:
int hours, minutes;
};
void Time::Time12()
{
if(hours>12) { cout<<hours-12<<":"<<minutes<<"PM\n" ; }
else cout<<hours<<":"<<minutes<<"AM\n" ;
}
void Time24(Time time)
{
cout<<time.hours<<":"<<time.minutes<<"\n";
}
void main()
{
Time T1(20,30), T2(10,45);
T1.Time12(); Time24(T1); T2.Time12(); Time24(T2);
}