C++ primer plus(第六版)编程练习答案 第15章 友元、异常和其他

一、程序清单

tv.h 

// tv.h -- Tv and Remote classes
#ifndef TV_H_
#define TV_H_

class Tv
{
public:
	friend class Remote;   // Remote can access Tv private parts
	enum { Off, On };
	enum { MinVal, MaxVal = 20 };
	enum { Antenna, Cable };
	enum { TV, DVD };

	Tv(int s = Off, int mc = 125) : state(s), volume(5),
		maxchannel(mc), channel(2), mode(Cable), input(TV) {}
	void onoff() { state = (state == On) ? Off : On; }
	bool ison() const { return state == On; }
	bool volup();
	bool voldown();
	void chanup();
	void chandown();
	void set_mode() { mode = (mode == Antenna) ? Cable : Antenna; }
	void set_input() { input = (input == TV) ? DVD : TV; }
	void settings() const; // display all settings
private:
	int state;             // on or off
	int volume;            // assumed to be digitized
	int maxchannel;        // maximum number of channels
	int channel;           // current channel setting
	int mode;