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C++primer（第五版）习题答案_c++primer第五版答案

作者：小蓝xlanll | 2024-05-02 00:28:03

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c++primer第五版答案

前两章习题较简单，这里就不作整理了，直接从第三章开始(持续更新)：

Chapter 3. Strings, Vectors and Arrays

Exercise 3.1

part 1

  1. #include <iostream>
  2.  
  3. using std::cin;
  4. using std::cout;
  5. using std::endl;
  6.  
  7. int main()
  8. {
  9.     int sum = 0, val = 1;
  10.     while (val <= 10) {
  11.         sum += val;
  12.         ++val;
  13.     }
  14.     cout << "Sum of 1 to 10 inclusive is " << sum << endl;
  15.     return 0;
  16. }

part 2

  1. #include <iostream>
  2.  
  3. using std::cin;
  4. using std::cout;
  5. using std::endl;
  6. using std::cerr;
  7.  
  8. struct Sales_data   {
  9.     std::string bookNo;
  10.     unsigned unit_sold = 0;
  11.     double revenue = 0.0;
  12. };
  13.  
  14. int main()
  15. {
  16.     Sales_data data1, data2;
  17.     double price = 0;
  18.     cin >> data1.bookNo >> data1.unit_sold >> price;
  19.     data1.revenue = data1.unit_sold * price;
  20.     cin >> data2.bookNo >> data2.unit_sold >> price;
  21.     data2.revenue = data2.unit_sold * price;
  22.     if (data1.bookNo == data2.bookNo)   {
  23.         unsigned totalCnt = data1.unit_sold + data2.unit_sold;
  24.         double totalRevenue = data1.revenue + data2. revenue;
  25.         cout << data1.bookNo << " " << totalCnt << " " << totalRevenue << " ";
  26.         if (totalCnt != 0)
  27.             cout << totalRevenue/totalCnt << endl;
  28.         else
  29.             cout << "(no sale)" << endl;
  30.         return 0;
  31.     }
  32.     else{
  33.         cerr << "Data must refer to the same ISBN" << endl;
  34.         return -1;
  35.     } 
  36. }

Exercise 3.2

part 1

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string line;
  12.     while (getline(cin, line))  {
  13.         cout << line << endl;
  14.     }
  15.     return 0;
  16. }

part 2

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string word;
  12.     while (cin >> word)
  13.         cout << word << endl;
  14.     return 0;
  15. }

Exercise 3.3

string类输入运算符(>>)：忽视一切空格，从第一个非空格字符开始，到第一个空格结束；

getline()：包含换行符前的所有空格；

Exercise 3.4

part 1

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string st1, st2;
  12.     cin >> st1 >> st2;
  13.     if (st1 == st2)
  14.         cout << "The two strings are equal" << endl;
  15.     else if (st1 > st2)
  16.         cout << "The maximum string is " << st1 << endl;
  17.     else 
  18.         cout << "The maximum string is " << st2 << endl;   
  19.     return 0;
  20. }

part 2

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string st1, st2;
  12.     cin >> st1 >> st2;
  13.     if (st1.size() == st2.size())
  14.         cout << "The two strings have the same length " << endl;
  15.     else if (st1.size() > st2.size())
  16.         cout << "The longest string is " << st1 << endl;
  17.     else 
  18.         cout << "The longest string is " << st2 << endl;   
  19.     return 0;
  20. }

Exercise 3.5

part 1

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string total_str, str;
  12.     while (cin >> str)
  13.         total_str += str;
  14.     cout << "The concatenated string is " << total_str << endl;
  15.     return 0;
  16. }

part 2

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string total_str, str;
  12.     while (cin >> str)
  13.         if (total_str.empty())
  14.             total_str += str;
  15.         else
  16.             total_str += " " +str;
  17.     cout << "The concatenated string is " << total_str << endl;
  18.     return 0;
  19. }

Exercise 3.6

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string str("I wanna go home!");
  12.     for (auto &c : str)  {
  13.         c = 'X';
  14.     }
  15.         
  16.     cout << str << endl;
  17.     return 0;
  18. }

Exercise 3.7

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string str("I wanna go home!");
  12.     for (char c : str)  {
  13.         c = 'X';
  14.     }   
  15.     cout << str << endl;
  16.     return 0;
  17. }
  18. //输出仍为I wanna go home!

本质上是把string中的每一个字符拷贝给循环控制变量c，此时对c更改只是改变了c字符，原string并没有任何变化，想要通过c改变string的值，就必须把c定义为对字符的引用。

Exercise 3.8

part 1

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string str("I wanna go home!");
  12.     decltype(str.size()) n = 0; //这里注意必须初始化
  13.     while ( n < str.size()) {
  14.         str[n] = 'X';
  15.         ++n;
  16.     }
  17.     cout << str << endl;
  18.     cout << n << endl;
  19.     return 0;
  20. }

part 2

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     string str("I wanna go home!");
  12.     for ( decltype(str.size()) index = 0; index < str.size(); ++index)  {
  13.         str[index] = 'X';
  14.     }
  15.     cout << str << endl;
  16.     return 0;
  17. }

使用范围for语句更简洁，逻辑也更清晰。

Exercise 3.9

不合法，不能用下标访问空字符串。

Exercise 3.10

  1. #include <iostream>
  2. #include <string>
  3.  
  4. using std::string;
  5. using std::cin;
  6. using std::cout;
  7. using std::endl;
  8.  
  9. int main()
  10. {
  11.     cout << "Please input a string with punctuation: " << endl;
  12.     string str, result;
  13.     cin >> str;
  14.     if (!str.empty())   {
  15.         for (auto &c : str)  {
  16.             if ( !ispunct(c))
  17.                 result += c;
  18.         }
  19.         cout << result << endl;
  20.         return 0;
  21.     }
  22.     cout << "Your string is fucking empty!" << endl;
  23.     return -1;
  24. }

注：这里使用ispunct()但不Include <cctype>是因为iostream中间接包含了cctype。

Exercise 3.11

c为常量字符串的引用（底层const）,只读取数据——合法，通过其修改数据——不合法。

Exercise 3.12

（a）正确，元素为向量，元素的元素为int；

（b）错误，拷贝初始化类型必须统一；

（c）正确，向量拥有10个空字符串元素；

Exercise 3.13

（a）无元素；

（b）10个元素，值均为0；

（c）10个元素，值均为42；

（d）一个元素，值为10；

（e）两个元素，值分别为10、42；

（f）10个元素，均为空字符串；

（g）10个元素，均为"hi"；

Exercise 3.14

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.    vector<int> ivec;
  14.    int i;
  15.    while (cin >> i) {
  16.        ivec.push_back(i);
  17.     return 0;
  18.    }
  19. }

Exercise 3.15

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.    vector<string> svec;
  14.    string str;
  15.    while (cin >> str) {
  16.        svec.push_back(str);
  17.     return 0;
  18.    }
  19. }

Exercise 3.16:

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     //v1
  14.    vector<int> v1;
  15.     cout << "The size is: "<< v1.size() << endl;
  16.     cout <<  "The value is: ";
  17.     for (auto i : v1)
  18.         cout << i << " ";     
  19.     cout << endl;
  20.     //v2
  21.     vector<int> v2(10);
  22.     cout << "The size is: "<< v2.size() << endl;
  23.     cout <<  "The value is: ";
  24.     for (auto i : v2)
  25.         cout << i << " ";     
  26.     cout << endl;
  27.     //后续同理
  28. }

Exercise 3.17

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     vector<string> text;
  14.     string word;
  15.     while (cin >> word) {
  16.         text.push_back(word);
  17.     }
  18.     cout << "The original text is: " << endl;
  19.     for (auto i : text) {
  20.         cout << i << endl;
  21.     }
  22.     cout << "The changed text is: " << endl;
  23.     for (auto str : text) {
  24.         for (auto &c : str)  {
  25.             c = toupper(c);
  26.         }
  27.         cout << str << endl;
  28.     }
  29.     return 0;
  30. }

Exercise 3.18

不合法，不能使用无效下标访问不存在的元素。修改如下：

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     ivec.push_back(42);
  15.     cout << ivec[0] << endl;
  16.     return 0;
  17. }

Exercise 3.19

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec1(10, 42);
  14.     vector<int> ivec2{42, 42, 42, 42, 42, 42, 42, 42, 42, 42};
  15.     vector<int> ivec3;
  16.     for (auto i = 0; i != 10; ++i)
  17.         ivec3.push_back(42);
  18.     vector<string> svec1{10, "42"};
  19.     vector<string> svec2(10, "42");
  20.     return 0;
  21. }

ivec1的定义方式简洁且高效。

Exercise 3.20

part 1:

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     int i = 0, sum = 0;
  15.     while (cin >> i)
  16.         ivec.push_back(i);
  17.     if (ivec.empty())   {    //因为后续用到下标，这里必须验证是否为空！！
  18.         cout << "Please input at least one integer"<< endl;
  19.         return -1;
  20.     }
  21.     cout << "The sum is: " << endl;
  22.     for (decltype(ivec.size()) index = 0; index < ivec.size() - 1; ++index)    {
  23.         sum = ivec[index]+ ivec[index + 1];
  24.         cout << sum << " ";
  25.     }
  26.     cout << endl;
  27.     return 0;
  28. }

part 2:

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     int i = 0, sum = 0;
  15.     while (cin >> i)
  16.         ivec.push_back(i);
  17.     if (ivec.empty())   {
  18.         cout << "Please input at least one integer"<< endl;
  19.         return -1;
  20.     }
  21.     cout << "The sum is: " << endl;
  22.     for (decltype(ivec.size()) index = 0; index <= ivec.size()/2; ++index)    {
  23.         if (index < ivec.size() - 1 - index)    {
  24.             sum = ivec[index]+ ivec[ivec.size() - 1 - index];
  25.             cout << sum << " ";
  26.         }
  27.         else if (index == ivec.size() - 1 - index)   {  //这里一定注意为双等号！！
  28.             cout << ivec[index];
  29.         }
  30.     }
  31.     cout << endl;
  32.     return 0;
  33. }

Exercise 3.21

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     //以v2为例，其他同理
  14.     vector<int> v2(10);
  15.     if (v2.empty()) {
  16.         cout << "This is a empty vector " << endl;
  17.         return -1;
  18.     }
  19.     cout << "The size of the vector is: " << v2.size() << endl;
  20.     cout << "The values of the elements are: ";
  21.     for (auto it = v2.cbegin(); it != v2.cend(); ++it)  {
  22.         cout << *it << " ";
  23.     }
  24.     cout << endl;
  25.     return 0;
  26. }

Exercise 3.22

  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4.  
  5. using std::string;
  6. using std::cin;
  7. using std::cout;
  8. using std::endl;
  9. using std::vector;
  10.  
  11. int main()
  12. {
  13.     cout << "Please enter a text: " << endl;
  14.     vector<string> svec;
  15.     string str;
  16.     while (getline(cin, str))
  17.         svec.push_back(str);
  18.     auto it = svec.begin();
  19.     for (auto &c : *it)
  20.         c = toupper(c);
  21.     for (it;it != svec.cend(); ++it)    //注意这里it可不重新定义，但不能省略！！
  22.         cout << *it << endl;
  23.     return 0;
  24. }

Exercise 3.23

  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. using std::vector;
  6. using std::string;
  7. using std::cout;
  8. using std::cin;
  9. using std::endl;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec(10);
  14.     int i;
  15.     cout << "Please enter ten integers: " << endl;
  16.     for (auto it = ivec.begin(); it != ivec.cend(); ++it)   {
  17.         cin >> *it;
  18.         *it *= 2;
  19.     }
  20.     for (auto i : ivec)
  21.         cout << i << " ";
  22.     cout << endl;
  23.     return 0;
  24. }

Exercise 3.24

part 1

  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. using std::vector;
  6. using std::string;
  7. using std::cout;
  8. using std::cin;
  9. using std::endl;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     int i;
  15.     while (cin >> i)
  16.         ivec.push_back(i);
  17.     cout << "The sum is: " << endl;
  18.     for (auto it = ivec.cbegin(); it != ivec.cend() - 1; ++it)
  19.         cout << *it + *(it + 1) << " ";
  20.     cout << endl;
  21.     return 0;
  22. }

part 2

法I：

  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. using std::vector;
  6. using std::string;
  7. using std::cout;
  8. using std::cin;
  9. using std::endl;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     int i, sum;
  15.     while (cin >> i)
  16.         ivec.push_back(i);
  17.     if (ivec.empty())
  18.         cout << "Your vector is empty!" << endl;
  19.     cout << "The sum is: " << endl;
  20.     for (auto it = ivec.cbegin(); it != ivec.cbegin() + ivec.size()/2 +1; ++it) {
  21.         if (it == ivec.cbegin() + (ivec.cend() - 1 - it))    {
  22.             cout << *it;
  23.         }
  24.         else if (it < ivec.cbegin() + (ivec.cend() - 1 - it))   {
  25.             sum = *it + *(ivec.cbegin() + (ivec.cend() - 1 - it));
  26.             cout << sum << " ";
  27.         }
  28.     }
  29.     cout << endl;
  30.     return 0;
  31. }

法II：

  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. using std::vector;
  6. using std::string;
  7. using std::cout;
  8. using std::cin;
  9. using std::endl;
  10.  
  11. int main()
  12. {
  13.     vector<int> ivec;
  14.     int i, sum;
  15.     while (cin >> i)
  16.         ivec.push_back(i);
  17.     if (ivec.empty())
  18.         cout << "Your vector is empty!" << endl;
  19.     cout << "The sum is: " << endl;
  20.     for (auto beg = ivec.cbegin(), end = ivec.cend()  - 1; beg <= end; ++beg, --end)    {   //注意方法！！
  21.         if (beg == end)
  22.             cout << *beg;
  23.         else
  24.             cout << *beg + *end << " ";
  25.     }
  26.     cout << endl;
  27.     return 0;
  28. }

Exercise 3.25

  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. using std::vector;
  6. using std::string;
  7. using std::cout;
  8. using std::cin;
  9. using std::endl;
  10.  
  11. int main()
  12. {
  13.     vector<unsigned> scores(11, 0);
  14.     unsigned grade;
  15.     auto it = scores.begin(); 
  16.     while (cin >> grade)    {
  17.         if (grade <= 100)   {
  18.             ++*(scores.begin() + grade/10);
  19.         }
  20.     }
  21.     for (auto i : scores)
  22.         cout << i << " ";
  23.     cout << endl;
  24.     return 0;
  25. }

Exercise 3.26

两个迭代器间只定义了相见，未定义相加；

所以可通过利用iterator - iterator将iterator +iterator转化为iterator + n。

Exercise 3.27

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