C++ Primer Plus 第十八章 课后编程练习题

//1题//
#include < iostream>
#include < initializer_list>
template< typename T>
T average_list(std::initializer_list l)
{
T tot = 0;
for (auto p = l.begin(); p != l.end(); p++)
{
tot += *p;
}
T aver = tot / l.size();
return aver;
}

int main()
{
using namespace std;
auto q = average_list({15.4, 10.7, 9.0});
cout << q << endl;
cout << average_list({20, 30, 19, 17 ,45, 38}) << endl;
auto aq = average_list({‘A’, 70, 65.33});
cout << aq << endl;

return 0;

}
//2题
#include < iostream>
#include < string>
static int ct = 0;
class Cpmv
{
public:
struct Info
{
std::string qcode;
std::string zcode;
};
private:
Info *pi;
public:
Cpmv();
Cpmv(std::string & q, std::string & z);
Cpmv(const Cpmv & cp);
Cpmv(Cpmv && mv);
~Cpmv();
Cpmv & operator=(const Cpmv & cp);
Cpmv & operator=(Cpmv && mv);
Cpmv operator+(const Cpmv & obj)const;
void ShowObject() const;
void ShowData() const;
};

Cpmv::Cpmv()
{
++ct;
pi = new Info;
pi->qcode = “Null!”;
pi->zcode = “Null!”;
std::cout << ct <<": 调用无参数默认构造函数!\n";
ShowObject();
}

Cpmv::Cpmv(std::string &q, std::string & z)
{
++ct;
pi = new Info;
pi->qcode = q;
pi->zcode = z;
std::cout << ct <<": 调用两个string参数的构造函数!\n";
ShowObject();
}

Cpmv::Cpmv(const Cpmv & cp)
{
++ct;
pi = new Info;
pi->qcode = cp.pi->qcode;
pi->zcode = cp.pi->zcode;
std::cout << ct <<": 调用复制构造函数!\n";
ShowObject();
}

Cpmv::Cpmv(Cpmv && mv)
{
++ct;
pi = mv.pi;
mv.pi = nullptr;
std::cout << ct <<": 调用移动复制构造函数!\n";
ShowObject();
}

Cpmv::~Cpmv()
{
std::cout << --ct <<": 调用析构函数!\n";
ShowObject();
delete pi;

}

Cpmv & Cpmv::operator=(const Cpmv & cp)
{
pi = new Info;
pi->qcode = cp.pi->qcode;
pi->zcode = cp.pi->zcode;
return *this;
}

Cpmv & Cpmv::operator=(Cpmv && mv)
{
pi = mv.pi;
mv.pi = nullptr;
return *this;
}

Cpmv Cpmv::operator+(const Cpmv & cp) const
{
Cpmv p;
p.pi->qcode = pi->qcode + cp.pi->qcode;
p.pi->zcode = pi->zcode + cp.pi->zcode;
p.ShowObject();
return p;
}

void Cpmv::ShowObject() const
{
std::cout << (void *) pi << std::endl;
}

void Cpmv::ShowData() const
{
std:: cout << pi->qcode <<" " << pi->zcode << std::endl;
}
int main()
{
std::string a, b;
a = “aaaaa”;
b = “bbbbb”;
Cpmv one(a, b);
Cpmv two = one;
Cpmv three(b, a);
Cpmv four (one + three);

std::cout <<"one: ";
one.ShowData();
std::cout <<"two: ";
two.ShowData();
std::cout <<"three: ";
three.ShowData();
std::cout <<"four: ";
four.ShowData();
return 0;

}

//3题

#include < iostream>

long double sum_value()
{
return 0;
}
template <typename T, typename … Args>
long double sum_value(const T &s,const Args & … args)
{
long double d;
d = (double)s+ sum_value(args …);
return d;
}

int main()
{
std::cout << sum_value(7, 9, 78.9) << std::endl;
return 0;
}

//4题//
//需要修改的应该是16.15 而不是书上说的16.5
#include < iostream>
#include < list>
#include < iterator>
#include < algorithm>

int main()
{
using std::list;
using std::cout;
using std::endl;
int vals[10] = {50, 100, 90, 180, 60, 210, 415, 88, 188, 201};
list yadayada(vals, vals + 10);
list etcetera(vals, vals + 10);
auto outint = [] (int x) { cout << x <<" ";};
cout <<“original lists:\n”;
for_each(yadayada.begin(), yadayada.end(), outint);
cout << endl;
for_each(etcetera.begin(), etcetera.end(), outint);
cout << endl;
yadayada.remove_if([](int x) {return x > 100;});
etcetera.remove_if([](int x) {return x > 200;});
cout <<“Trimmed lists:\n”;
for_each(yadayada.begin(), yadayada.end(), outint);
cout << endl;
for_each(etcetera.begin(), etcetera.end(), outint);
cout << endl;

return 0;

}