c++ primer plus 第六版第十五章编程练习
- 对书本实例中的Tv类和Remote类进行修改，使互为友元，在Remote类中添加状态成员描述处于常规模式还是互动模式，并添加显示模式的方法；Tv类添加对Remote类新成员进行切换的方法（仅当电视处于打开状态时使用）
注意：由于在Tv类中有函数state_switch()动用Remote类对象来访问成员，所以要有个提前声明给Remote类：
class Remote
不然就会在编译中出现关于函数state_switch没声明之类的错误。
#include 方法声明
#include "tv.h"
//Tv methods
bool Tv::volup()
{
if (volume < MaxVal)
{
volume++;
return true;
}
else
return false;
}
bool Tv::voldown()
{
if (volume > 0)
{
volume--;
return true;
}
else
return false;
}
void Tv::chanup()
{
if (channel < maxchannel)
channel++;
else
channel = 1;
}
void Tv::chandown()
{
if (channel > 0)
channel--;
else
channel = maxchannel;
}
void Tv::settings() const
{
using std::cout;
using std::endl;
cout << "TV is " << (state == Off ? "Off" : "On") << endl;
if (state == On)
{
cout << "Volume setting =" << volume << endl;
cout << "Channel setting: " << channel << endl;
cout << "Mode :" << (mode == Antenna ? "antenna" : "cable") << endl;
cout << "Input: " << (input == TV ? "TV" : "DVD") << endl;
}
}
测试程序
#include 测试程序是书本中的，稍微加了新增方法的演示。对于互动我也不知道怎么互动了，干脆给一个输出和一个响铃来作为提示“互动模式”了，注意：响铃真的很小声，我带了耳机才听到。
- 修改程序15.11，使得两种异常类型为从头文件stdexcept提供的logic_error类派生出来的类。
声明头文件
#include 测试程序
#include :"
;
}
catch (bad_hmean &h)
{
cout << h.what();
cout << "Values used: " << h.v1 << ", " << h.v2 << endl;
cout << "Try again.\n";
continue;
}
catch (bad_gmean &g)
{
cout << g.what();
cout << "Values used: " << g.v1 << ", " << g.v2 << endl;
cout << "Sorry,you don't get to play any more." << endl;
break;
}
}
cout << "Bye." << endl;
system("pause");
return 0;
}
double hmean(double a, double b)
{
if (a == -b)
throw bad_hmean(a, b);
return 2.0 * a * b / (a + b);
}
double gmean(double a, double b)
{
if (a < 0 || b < 0)
throw bad_gmean(a, b);
return std::sqrt(a * b);
}
原来的例子是声明定义类成员函数来输出提示信息，把异常类logic_error以基类加进来后就使用其自带的what函数来返回字符串提示，在程序catch语块中输出就行。
- 同样是改动15.11，但异常类是从logic_error派生而来的基类，存储两个参数，有一个可以报告参数值和调用函数名的成员函数。测试程序使用catch捕获异常，任何一种从基类异常派生而来的异常都将导致循环结束。
#include #include :"
;
}
catch (badbad &bb)
{
cout << bb.what();
cout << "Values used: " << bb.v1 << ", " << bb.v2 << endl;
cout << "Sorry,byebye." << endl;
break;
}
}
cout << "Enter two numbers: ";
while (cin >> x >> y)
{
try
{
z = gmean(x, y);
cout << "Geometric mean of " << x << " and " << y
<< " is " << z << endl;
cout << "Enter next set of numbers :"
;
}
catch (badbad &bb)
{
cout << bb.what();
cout << "Values used: " << bb.v1 << ", " << bb.v2 << endl;
cout << "Sorry,you don't get to play any more." << endl;
break;
}
}
cout << "Bye." << endl;
system("pause");
return 0;
}
double hmean(double a, double b)
{
if (a == -b)
throw badbad("Invalid argument for hmean().\n", a, b);
return 2.0 * a * b / (a + b);
}
double gmean(double a, double b)
{
if (a < 0 || b < 0)
throw badbad("Invalid argument for gmean().\n", a, b);
return std::sqrt(a * b);
}
不太明白题目所说的显示函数在这里的意义，我干脆不做编写。
- 把程序清单里15.16里的模式修改，使得不需要每个try后面都跟两个catch而只用一个catch并用RTTI来确保合适时调用label_val()
#include 方法声明
#include "sales.h"
//Sales methods
Sales::Sales(int yy)
{
year = yy;
for (int i = 0; i < MONTHS; i++)
gross[i] = 0;
}
Sales::Sales(int yy, const double *gr, int n)
{
year = yy;
int lim = (n < MONTHS) ? n : MONTHS;
int i;
for (i = 0; i < lim; ++i)
gross[i] = gr[i];
for (; i < MONTHS; ++i)
gross[i] = 0;
}
double Sales::operator[](int i) const
{
if (i < 0 || i >= MONTHS)
throw bad_index(i);
return gross[i];
}
double &Sales::operator[](int i)
{
if (i < 0 || i >= MONTHS)
throw bad_index(i);
return gross[i];
}
//LabeledSales methods
double LabeledSales::operator[](int i) const
{
if (i < 0 || i >= MONTHS)
throw nbad_index(Label(), i);
return Sales::operator[](i);
}
double &LabeledSales::operator[](int i)
{
if (i < 0 || i >= MONTHS)
throw nbad_index(Label(), i);
return Sales::operator[](i);
}
测试程序
#include 