C++ Primer Plus 第六版（中文版）课后编程题----第八章

8.1

一开始并不太理解题目中“打印该字符串的字数为该函数被调用的次数”，于是参考了一篇博文：http://blog.csdn.net/qq844352155/article/details/23349027

#include <iostream>
using namespace std;

void print(const char *str, int n = 0);
int num = 0;

int main()
{
	print("There is no second parameter!");
	print("The second parameter is zero!", 0);
	print("The second parameter is not zero", 1);
	print("Done!", 100000);
	system("pause");
	return 0;
}

void print(const char *str, int n)
{
	if (num == 0)
		cout << str << endl;
	else
	{
		for (int i = 0; i < num; ++i)
			cout << str << endl;
	}
	++num;
}

8.2

#include <iostream>
#include <string>
using namespace std;

struct CandyBar
{
	char brand[50];
	double weight;
	int calories;
};

void assignin(CandyBar & candy, const char *str = "Millenmum Munch", const double d = 2.85, const int n = 350);
void display(const CandyBar & candy);

int main()
{
	CandyBar bar;
	
	assignin(bar);
	cout << "The original information of Candy Bar is: " << endl;
	display(bar);

	assignin(bar, "Candy Bar", 3.69, 920);
	cout << "The latest information of Candy Bar is: " << endl;
	display(bar);

	system("pause");
	return 0;
}

void assignin(CandyBar & candy, const char *str, const double d, const int n)
{
	strcpy_s(candy.brand,str);
	candy.weight = d;
	candy.calories = n;
}

void display(const CandyBar & candy)
{
	cout << "Brand is: " << candy.brand << endl;
	cout << "Weight is: " << candy.weight << endl;
	cout << "Calories is: " << candy.calories << endl;
}

8.3

#include <iostream>
#include <string>
#include <cctype>
using namespace std;

void Transfor(string & str);

int main()
{
	string str;
	cout << "Please enter a string(q to quit): ";
	while ((getline(cin,str)) && str != "q")
	{
		Transfor(str);
		cout << str << endl;
		cout << "Next string(q to quit): ";
	}
	cout << "Bye." << endl;
	system("pause");
	return 0;
}

void Transfor(string & str)
{
	for (int i = 0; i < str.size(); ++i)
		str[i] = toupper(str[i]);
}

8.4

set 函数中不能使用 const char * ch 作为第二个形参，否则在函数定义中无法直接对 string 进行赋值。

#include <iostream>
#include <string>
using namespace std;
struct stringy
{
	char * st;
	int ct;
};

void set(stringy &str, char *ch);
void show(const char *str, const int n = 1);
void show(const stringy &str, const int n = 1);

int main()
{
	stringy beany;
	char testing[] = "Reality isn't what it used to be.";

	set(beany, testing);
	show(beany);
	show(beany, 2);

	testing[0] = 'D';
	testing[1] = 'u';
	show(testing);
	show(testing, 3);
	show("Done!");

	system("pause");
	return 0;
}

void set(stringy &str, char * ch)
{
	str.ct = strlen(ch);
	str.st = ch;
}

void show(const stringy &str, const int n)
{
	for (int i = 0; i < n; ++i)
		cout << str.st << endl;
}
void show(const char * str, const int n)
{
	for (int i = 0; i < n; ++i)
		cout << str << endl;
}

8.5

题中说的是固定长度为 5，此处我仍旧设置了一个可变的长度，如果只需固定长度，那 max5 函数中的第二个参数可省略。（后面才知道第六题中是可变长度，据此可以修改）

#include <iostream>
using namespace std;

const int num = 5;

template <typename T>
T max5(T * arr, const int n = num);<span style="white-space:pre">	</span>//固定长度的话可以修改为 <span style="font-family: Arial, Helvetica, sans-serif;">T max5(T * arr);</span>

int main()
{
	int arr_i[num] = { 1, 5, 2, 3, 6 };
	double arr_d[num] = { 1.6, 2.5, 9.8, 6.3, 2.3 };

	cout << "The max of five int numbers is: " << max5(arr_i) << endl;
	cout << "The max of five double number is: " << max5(arr_d) << endl;

	system("pause");
	return 0;
}

template <typename T>
T max5(T * arr, const int n)<span style="white-space:pre">	</span>//固定长度此处修改为：<span style="font-family: Arial, Helvetica, sans-serif;">T max5(T * arr);</span>

{
	if (n == 0)<span style="white-space:pre">		</span>//固定长度中这个判断可以省略，也没有 n 的存在了。
		return 0;
	T max_num = arr[0];
	for (int i = 1; i < n; ++i)<span style="white-space:pre">	</span>//固定长度此处修改为 <span style="font-family: Arial, Helvetica, sans-serif;">for (int i = 1; i < num; ++i)</span>

		max_num = max_num>arr[i] ? max_num : arr[i];
	return max_num;
}

8.6

注意：具体化的模板和非具体化的模板格式必须完全一致。下面两种情况都是不可行的。

情况一：

//非具体化模板
template <typename T>
T maxn(const T * arr, const int n);

//具体化模板
template <> char *maxn<char *>(char *p[], const int n);

情况二：

//非具体化模板
template <typename T>
T maxn(const T * arr, const int n);

//具体化模板
template <> const char *maxn<char *>(const char *p[], const int n);

正确的应该是：

#include <iostream>
using namespace std;

template <typename T>
T maxn(T * arr, const int n);
template <> char *maxn<char *>(char *p[], const int n);

int main()
{
	int arr_i[6] = { 1, 5, 2, 3, 6, 9 };
	double arr_d[4] = { 1.6, 2.5, 9.8, 6.3 };
	char *p[5] = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };

	cout << "The max of five int numbers is: " << maxn(arr_i, 6) << endl;
	cout << "The max of five double number is: " << maxn(arr_d, 4) << endl;
	cout << "The max length of the string is: " << maxn(p, 5) << endl;

	system("pause");
	return 0;
}

template <typename T>
T maxn(T * arr, const int n)
{
	if (n == 0)
		return 0;
	T max_num = arr[0];
	for (int i = 1; i < n; ++i)
		max_num = max_num>arr[i] ? max_num : arr[i];
	return max_num;
}

template <> char *maxn<char *>(char *p[], const int n)
{
	if (n == 0)
		return nullptr;
	char *pt = p[0];
	for (int i = 1; i < n; ++i)
		pt = strlen(pt)>strlen(p[i]) ? pt : p[i];
	return pt;
}

8.7

#include <iostream>
using namespace std;

template <typename T>
T SumArray(T arr[], int n);

template <typename T>
T SumArray(T *arr[], int n);

struct debts
{
	char name[50];
	double amount;
};

int main()
{
	int things[6] = { 13, 31, 103, 301, 310, 130 };
	struct debts mr_E[3]=
	{
		{ "Ima Wolfe", 2400.5 },
		{ "Ura Foxe", 1300.3 },
		{ "Iby Stout",1800.4 }
	};
	double *pd[3];

	for (int i = 0; i < 3; ++i)
		pd[i] = &mr_E[i].amount;
	cout << "Total Mr. E's counts of things is: " << SumArray(things, 6) << endl;
	cout << "Total Mr. E's debts is: " << SumArray(pd, 3) << endl;

	system("pause");
	return 0;
}

template <typename T>
T SumArray(T arr[], int n)
{
	cout << "template A\n";
	T sum = T(0);
	for (int i = 0; i < n; ++i)
		sum += arr[i];
	return sum;
}

template <typename T>
T SumArray(T *arr[], int n)
{
	cout << "template B\n";
	T sum = T(0);
	for (int i = 0; i < n; ++i)
		sum += *arr[i];
	return sum;
}