C++ Primer第5版 第三章课后练习答案

练习3.1

#include <iostream>
using namespace std;
int main()
{
    int sum = 0, val = 50;
    while (val <= 100) {
        sum += val;
        ++val;
    }
    cout << "Sum of 50 to 100 inclusive is " << sum << std::endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int val = 10;
    while (val >= 0) {
        cout << val-- << std::endl;
    }
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    cout << "Please enter the two integers" << endl;
    int start, end;
    //我这里没有对传入格式进行判断，如果大家有需要可以添加这个功能
    cin >> start >> end;
    if (start > end) {
        swap(start, end);
    }
    while (start <= end) {
        cout << start++ << endl;
    }
    return 0;
}

#include<iostream>
using namespace std;
struct Sales_data {
    string bookNo;
    unsigned units_sold = { 0 };
    double revenue = { 0.0 };
};
int main()
{
    Sales_data data;
    double price;
    while (cin >> data.bookNo >> data.units_sold >> price) {
        data.revenue = data.units_sold * price;
        cout << "Record:" << data.bookNo << " " << data.units_sold << " " << data.revenue << endl;
    }
}

#include  <iostream>
using namespace std;
struct Sales_data {
    string bookNo;
    unsigned units_sold = { 0 };
    double revenue = { 0.0 };
};
int main()
{
    Sales_data data1, data2;
    double price;
    if (cin >> data1.bookNo >> data1.units_sold >> price) {
        data1.revenue = data1.units_sold * price;
    }
    if (cin >> data2.bookNo >> data2.units_sold >> price) {
        data2.revenue = data2.units_sold * price;
    }
    if (data1.bookNo == data2.bookNo) {
        unsigned totalCnt = data1.units_sold + data2.units_sold;
        double totalRevenue = data1.revenue + data2.revenue;
        cout << data1.bookNo << " " << totalCnt << " " << totalRevenue << endl;
        return 0;
    }
    else {
        return -1;
    }
}

#include  <iostream>
using namespace std;
struct Sales_data {
    string bookNo;
    unsigned units_sold = { 0 };
    double revenue = { 0.0 };
};
int main()
{
    Sales_data data1, data2;
    unsigned totalCnt = 0;
    double totalRevenue = 0.0;
    double price;
    while (cin >> data1.bookNo >> data1.units_sold >> price) {
        data1.revenue = data1.units_sold * price;
        totalCnt += data1.units_sold;
        totalRevenue += data1.revenue;
    }
    cout << data1.bookNo << " " << totalCnt << " " << totalRevenue << endl;
    return 0;
}

#include  <iostream>
using namespace std;
struct Sales_data {
    string bookNo;
    unsigned units_sold = { 0 };
    double revenue = { 0.0 };
};
int main()
{
    Sales_data data1, data2;
    double price;
    if (cin >> data1.bookNo >> data1.units_sold >> price) {
        data1.revenue = data2.units_sold * price;
        int cnt = 1;
        while (cin >> data2.bookNo >> data2.units_sold >> price) {
            data1.revenue = data2.units_sold * price;
            if (data1.bookNo == data2.bookNo)
                cnt++;
            else {
                cout << data1.bookNo << " " << cnt << endl;
                cnt = 1;
                data1 = data2;
            }
        }
        cout << data1.bookNo << " " << cnt << endl;
    }
    return 0;
}

练习3.2

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str,line;
    //一次读入一整行
    while (getline(cin, line)) {
        str = str + line;
    }
    cout << str;
    return 0;
}

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str,line;
    //一次读入一个词
    while (cin>>line) {
        str = str + line;
    }
    cout << str;
    return 0;
}

练习3.3

输入运算符会自动忽略开头的空白并从第一个真正的字符读起，直到遇见下一处空白为止

getline会从给定的输入流中读入内容，保留输入时的空白符，直到遇到换行符为止

练习3.4

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str1,str2;
    //一次读入一整行
    cin >> str1 >> str2;
    if (str1 == str2)cout << "相等";
    else {
        cout << (str1 > str2 ? str1 : str2);
    }
    return 0;
}

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str1,str2;
    //一次读入一整行
    cin >> str1 >> str2;
    if (str1.size() == str2.size())cout << "相等";
    else {
        cout << (str1.size() > str2.size() ? str1 : str2);
    }
    return 0;
}

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str1,str2;
    //一次读入一整行
    cin >> str1 >> str2;
    if (str1.size() == str2.size())cout << "相等";
    else {
        cout << (str1.size() > str2.size() ? str1 : str2);
    }
    return 0;
}

练习3.5

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str1,str2;
    while (cin >> str1) {
        str2 += str1;
    }
    cout << str2;
    return 0;
}

#include  <iostream>
#include<string>
using std::cin;
using std::cout;
using std::string;
int main()
{
    string str1,str2;
    while (cin >> str1) {
        str1 += " ";
        str2 += str1;
    }
    cout << str2;
    return 0;
}

练习3.6

#include  <iostream>
#include<string>
using std::cout;
using std::string;
int main()
{
    string str="0123456789ABCDEF";
    for (auto& c : str) {
        c = 'X';
    }
    cout << str;
    return 0;
}

练习3.7

没有变化

#include  <iostream>
#include<string>
using std::cout;
using std::string;
int main()
{
    string str="0123456789ABCDEF";
    for (char& c : str) {
        c = 'X';
    }
    cout << str;
    return 0;
}

练习3.8

#include  <iostream>
#include<string>
using std::cout;
using std::string;
int main()
{
    string str="0123456789ABCDEF";
    decltype(str.size()) i = 0;
    while (i < str.size()) {
        str[i++] = 'X';
    }
    cout << str;
    return 0;
}

#include  <iostream>
#include<string>
using std::cout;
using std::string;
int main()
{
    string str="0123456789ABCDEF";
    for (auto i = 0; i < str.size();i++) {
        str[i] = 'X';
    }
    cout << str;
    return 0;
}

练习3.9

输出默认初始化字符串s的第一个元素。不合法，因为默认初始化的字符串是空串，所以s[0]越界了。

练习3.10

#include  <iostream>
#include<string>
using std::cout;
using std::string;
int main()
{
    string str="123()_+asad";
    for (string::size_type i = 0; i < str.size(); i++) {
        if (!ispunct(str[i]))
            cout << str[i];
    }
    return 0;
}

练习3.11

for循环体不看后面花括号的内容，肯定是合法的，但是如果在for循环中花括号中给C赋值，修改C的值，那么此时的for语句肯定是不合法的。C的类型是const char& 

练习3.12

知识点：vector的初始化：

1：引用不可以成为vector的元素，因为其不是对象。

2：可以用花括号初始化每一个值。

3：可以用括号指定元素个数或相同的元素值。

4：只能使用直接初始化，不可以使用拷贝初始化（vector之间的拷贝是可行的，但要保证类型相同）

答案：

(a)正确，创建了一个元素为vector的vector对象

(b)不正确，类型不一致

(c)正确，十个“null”对象

练习3.13

(a)空vector

(b)10个重复执行值初始化对象0

(c)10个重复的元素42

(d)1个元素初始值为10

(e)两个元素，初始分别为10,42

(f)10个字符串，初始化为“ ”（空）

(g)10个字符串，初始化为“hi ”

练习3.14

#include  <iostream>
#include<string>
#include <vector>
using std::cin;
using std::cout;
using std::vector;
int main()
{
    int num;
    vector<int> v;
    while (cin >> num) {
        v.push_back(num);
    }
    return 0;
}

练习3.15

#include  <iostream>
#include<string>
#include <vector>
using std::cin;
using std::cout;
using std::vector;
using std::string;
int main()
{
    string str;
    vector<string> v;
    while (cin >> str) {
        v.push_back(str);
    }
    return 0;
}

练习3.16

#include  <iostream>
using std::cin;
using std::cout;
using std::endl;

#include <vector>
using std::vector;

#include<string>
using std::string;

int main()
{
    vector<int> v1;
    vector<int> v2(10);
    vector<int> v3(10, 42);
    vector<int> v4{ 10 };
    vector<int> v5{ 10,42 };
    vector<string> v6{ 10 };
    vector<string> v7(10, "hi");
    cout << v1.size()<<" ";
    for (auto v1_item = v1.begin(); v1_item != v1.end(); v1_item++)
        cout << *v1_item << " ";

    cout << endl << v2.size() << " ";
    for (auto v2_item = v2.begin(); v2_item != v2.end(); v2_item++)
        cout << *v2_item << " ";

    cout << endl << v1.size() << " ";
    for (auto v3_item = v3.begin(); v3_item != v3.end(); v3_item++)
        cout << *v3_item << " ";

    cout << endl << v1.size() << " ";
    for (auto v4_item = v4.begin(); v4_item != v4.end(); v4_item++)
        cout << *v4_item << " ";

    cout << endl << v5.size() << " ";
    for (auto v5_item = v5.begin(); v5_item != v5.end(); v5_item++)
        cout << *v5_item << " ";

    cout << endl << v6.size() << " ";
    for (auto v6_item = v6.begin(); v6_item != v6.end(); v6_item++)
        cout << *v6_item << " ";

    cout << endl << v7.size() << " ";
    for (auto v7_item = v7.begin(); v7_item != v7.end(); v7_item++)
        cout << *v7_item << " ";
    return 0;
}

0
10 0 0 0 0 0 0 0 0 0 0
0 42 42 42 42 42 42 42 42 42 42
0 10
2 10 42
10
10 hi hi hi hi hi hi hi hi hi hi

练习3.17

#include  <iostream>
using std::cin;
using std::cout;
using std::endl;

#include <vector>
using std::vector;

#include<string>
using std::string;

int main()
{
    vector<string> v;
    string str;
    while (cin >> str) {
        v.push_back(str);
    }
    for (auto i = v.begin(); i != v.end(); i++) {
        str = *i;
        for (auto&c:str) {
            if (islower(c))
                c = toupper(c);
        }
        *i = str;
    }
    for (auto v_item : v) {
        cout << v_item << endl;
    }
    return 0;
}

练习3.18

不合法。

    vector<int> ivec;
    ivec.push_back(42);

练习3.19

    vector<int> v1(10, 42);
    vector<int> v2{ 42, 42,42, 42,42, 42,42, 42, 42, 42 };
    vector<int> v3 = v2;

第一种最好，比较简洁

练习3.20

#include  <iostream>
using std::cin;
using std::cout;
using std::endl;

#include <vector>
using std::vector;

int main()
{
    vector<int> v;
    int num;
    while (cin >> num) {
        v.push_back(num);
    }
    for (decltype(v.size()) i = 0; i < v.size() - 1; i++) {
        cout << (v[i] + v[i + 1]) << " ";
    }
    return 0;
}

#include  <iostream>
using std::cin;
using std::cout;
using std::endl;

#include <vector>
using std::vector;

int main()
{
    vector<int> v;
    int num;
    while (cin >> num) {
        v.push_back(num);
    }
    decltype(v.size()) j = v.size() - 1;
    for (decltype(v.size()) i = 0; i < v.size(); i++) {
        if (i < j - i)
            cout << (v[i] + v[j - i]) << " ";
    }
    return 0;
}

练习3.21

#include  <iostream>
using std::cin;
using std::cout;
using std::endl;

#include <vector>
using std::vector;

#include<string>
using std::string;

int main()
{
    vector<int> v1;
    vector<int> v2(10);
    vector<int> v3(10, 42);
    vector<int> v4{ 10 };
    vector<int> v5{ 10,42 };
    vector<string> v6{ 10 };
    vector<string> v7(10, "hi");
    cout << v1.size()<<" ";
    for (auto v1_item = v1.begin(); v1_item != v1.end(); v1_item++)
        cout << *v1_item << " ";

    cout << endl << v2.size() << " ";
    for (auto v2_item = v2.begin(); v2_item != v2.end(); v2_item++)
        cout << *v2_item << " ";

    cout << endl << v1.size() << " ";
    for (auto v3_item = v3.begin(); v3_item != v3.end(); v3_item++)
        cout << *v3_item << " ";

    cout << endl << v1.size() << " ";
    for (auto v4_item = v4.begin(); v4_item != v4.end(); v4_item++)
        cout << *v4_item << " ";

    cout << endl << v5.size() << " ";
    for (auto v5_item = v5.begin(); v5_item != v5.end(); v5_item++)
        cout << *v5_item << " ";

    cout << endl << v6.size() << " ";
    for (auto v6_item = v6.begin(); v6_item != v6.end(); v6_item++)
        cout << *v6_item << " ";

    cout << endl << v7.size() << " ";
    for (auto v7_item = v7.begin(); v7_item != v7.end(); v7_item++)
        cout << *v7_item << " ";
    return 0;
}

练习3.22

#include  <iostream>
using std::cin;
using std::cout;

#include <vector>
using std::vector;int main()
{
    vector<string> v;
    string str;
    if (getline(cin,str)) {
        v.push_back(str);
    }
    for (auto i = v.begin(); i != v.end(); i++) {
        str = *i;
        for (auto& c : str) {
            if (islower(c))
                c = toupper(c);
        }
        *i = str;
    }
    for (auto v_item : v) {
        cout << v_item << endl;
    }
    return 0;
}

练习3.23

#include  <iostream>
using std::cin;
using std::cout;

#include <vector>
using std::vector;

int main()
{
    vector<int> v;
    int num;
    for (unsigned i = 0; i < 10; i++) {
        cin >> num;
        v.push_back(num);
    }
    for (auto& v_item : v) {
        v_item *= 2;
    }
    for (auto v_item : v) {
        cout << v_item << " ";
    }
    return 0;
}

练习3.24

#include  <iostream>
using std::cin;
using std::cout;

#include <vector>
using std::vector;

int main()
{
    vector<int> v;
    int num;
    while (cin >> num) {
        v.push_back(num);
    }
    for (auto i = v.begin(), j = v.end() - 1; i < j; i++,j--) {
        cout << (*i + *j) << " ";
    }
    return 0;
}

练习3.25

#include  <iostream>
using std::cin;
using std::cout;

#include <vector>
using std::vector;

int main()
{
    vector<unsigned> scores(11,0);
    unsigned grade;
    while (cin >> grade) {
        if (grade <= 100) {
            auto it = (scores.begin() + grade / 10);
            (*it)++;
        }
    }
    return 0;
}

练习3.26

迭代器不支持除法运算

练习3.27

(a)非法，buf_size不是常量表达式

(c)非法，txt_size返回值是int而不是constexpr

练习3.28

在函数体外初始化

sa数组为空。

ia数组含有10个整数，皆为0。

在函数体内初始化

sa2数组为空。

ia2数组含有10个整数，值不确定。

练习3.29

数组的大小确定不变，不能随意向数组中增加元素，因此损失了一些灵活性

练习3.30

第三行"ix<=array_size"数组下标越界

练习3.31

#include  <iostream>

int main()
{
    int array_int[10];
    for (size_t i = 0; i < 10; i++) {
        array_int[i] = i;
    }
    return 0;
}

练习3.32

#include  <iostream>
using std::cout;

int main()
{
    int array_int[10];
    for (size_t i = 0; i < 10; i++) {
        array_int[i] = i;
    }
    int array_int2[10];
    for (size_t i = 0; i < 10; i++) {
        array_int2[i] = array_int[i];
    }
    return 0;
}

#include  <iostream>

#include<vector>
using std::vector;

int main()
{
    vector<int> array_int(10);
    auto array_int_item = array_int.begin();
    for (size_t i = 0; i < 10; i++) {
        *(array_int_item+i) = i;
    }
    vector<int> array_int2(array_int);
    return 0;
}

练习3.33

在函数体内不初始化值就是未知的。

练习3.34

将p1指向的元素修改为p2指向的元素，由于p1和p2指向同一个数组中的元素，所以没有改变。当p1或p2其中一个越界时该程序是非法的

练习3.35

#include  <iostream>


#include<iterator>
using std::begin;
using std::end;

int main()
{
    int array_int[10];
    auto* pend = end(array_int);
    for (auto pben = begin(array_int); pben != pend; pben++) {
        *pben = 0;
    }
    return 0;
}

练习3.36

template <typename _Container,unsigned N,unsigned M>
bool comptr(_Container(&ptr1)[N], _Container(&ptr2)[M]) {
    if (N == M) {//比较数组长度
        auto pend = end(ptr1);
        for (auto ptr1_item = ptr1, ptr2_item = ptr2; ptr1_item != pend; ptr1_item++, ptr2_item++) {
            if (*ptr1_item != *ptr2_item)return false;
        }
        return true;
    }
    return false;
}

template <typename _Container>
bool comptr(_Container(&ptr1), _Container(&ptr2)) {
    if (ptr1.size()==ptr2.size()) {
        for (auto ptr1_item = ptr1.begin(), ptr2_item = ptr2.begin(); ptr1_item != ptr1.end(); ptr1_item++, ptr2_item++) {
            if (*ptr1_item != *ptr2_item)return false;
        }
        return true;
    }
    return false;
}

练习3.37

h
e
l
l
o

练习3.38

指针指代的是对象的地址，相加是地址相加，难以区分到底什么意义。

练习3.39

C++风格的字符串比较是字符串本身的比较

C风格的字符串比较是字符串首地址的比较

练习3.40

#include <iostream>
#include <string>
#include <vector>
using namespace std;
void main()
{    
    char a[100] = "Hello World";
    char b[100] = "I want an apple";
    char c[200];
    strcpy(c,a);
    strcat(c," ");
    strcat(c,b);
    cout<<c;
}

练习3.41

#include  <iostream>
using std::cout;
using std::endl;

#include<iterator>
using std::begin;
using std::end;

#include <vector>
using std::vector;
    
int main()
{
    int array_int[] = { 0,1,2,3,4 };
    vector<int> v(begin(array_int), end(array_int));
}

练习3.42

void vector_to_array(vector<int>::iterator it, size_t& size) {
    int* array_int = new int[size];
    for (auto i = 0; i < size; i++) {
        array_int[i] = *(it + i);
        cout << array_int[i]<<" ";
    }
}

练习3.43

    for (int(&p)[4] : ia) {
        for (int q : p) {
            cout << q << " ";
        }
        cout << endl;
    }

    for (int p = 0; p < 3; p++) {
        for (int q = 0; q < 4; q++) {
            cout << ia[p][q] << " ";
        }
        cout << endl;
    }

    for (int(*p)[4] = ia; p < ia + 3; p++) {
        for (int* q = *p; q < *p + 4; q++) {
            cout << *q << " ";
        }
        cout << endl;
    }

练习3.44

    using int_array = int[4];
    for (int_array(&p) : ia) {
        for (int q : p) {
            cout << q << " ";
        }
        cout << endl;
    }

    for (int p = 0; p < 3; p++) {
        for (int q = 0; q < 4; q++) {
            cout << ia[p][q] << " ";
        }
        cout << endl;
    }

    for (int_array(*p) = ia; p < ia + 3; p++) {
        for (int* q = *p; q < *p + 4; q++) {
            cout << *q << " ";
        }
        cout << endl;
    }

练习3.45

    for (auto (&p) : ia) {
        for (auto q : p) {
            cout << q << " ";
        }
        cout << endl;
    }

    for (auto p = 0; p < 3; p++) {
        for (auto q = 0; q < 4; q++) {
            cout << ia[p][q] << " ";
        }
        cout << endl;
    }

    for (auto (*p) = ia; p < ia + 3; p++) {
        for (auto* q = *p; q < *p + 4; q++) {
            cout << *q << " ";
        }
        cout << endl;
    }