Chapter 3. Strings, Vectors, and Arrays

Exercise 3.1 : ex3_1

Exercise 3.2 : ex3_2

Exercise 3.3

Explain how whitespace characters are handled in the string input operator and in the getline function.

string读入时忽略开头的空白，从第一个真正的字符读起，到空白字符结束。 getline读入包括空白字符在内的字符，到换行符结束。

Exercise 3.4 : part1 | part2

Exercise 3.5 : part1 | part2

Exercise 3.6

Exercise 3.7

What would happen if you define the loop control variable in the previous exercise as type char? Predict the results and then change your program to use a char to see if you were right.

没有区别，推断出来也是 char 类型。

Exercise 3.8

范围for更好，使用简便，不用担心使用下标超出范围。

Exercise 3.9

What does the following program do? Is it valid? If not, why not?

string s;
cout << s[0] << endl;

不合法，s为空，s[0]的结果未定义。

Exercise 3.10

Exercise 3.11

Is the following range for legal? If so, what is the type of c?

const string s = "Keep out!";
for (auto &c : s){/*... */}

c的类型为 const char & ，如果改变了c的值则不合法。

Exercise 3.12

Which, if any, of the following vector definitions are in error? For those that are legal, explain what the definition does. For those that are not legal, explain why they are illegal.

vector<vector<int>> ivec;         // 合法(c++11)，旧版用vector<vector<int> > ivec。
vector<string> svec = ivec;       // 不合法，类型不匹配。
vector<string> svec(10, "null");  // 合法，10个值为"null"的string。

Exercise 3.13

How many elements are there in each of the following vectors? What are the values of the elements?

vector<int> v1;         // 空。
vector<int> v2(10);     // 10个0。
vector<int> v3(10, 42); // 10个42。
vector<int> v4{10};     // 1个10。
vector<int> v5{10, 42}; // 10和42。
vector<string> v6{10};  // 10个空。
vector<string> v7{10, "hi"};  // 10个"hi"。

Exercise 3.14

Exercise 3.15

Exercise 3.16

Exercise 3.17

Exercise 3.18

Exercise 3.19

第一种最好，理由如下：

简洁方便
直接构造，不占内存
不会溢出

Exercise 3.20

Exercise 3.21

Exercise 3.22

Exercise 3.23

Exercise 3.24

Exercise 3.25

Exercise 3.26

In the binary search program on page 112, why did we write mid=beg+(end-beg)/2; instead of mid=(beg+end) /2;?

迭代器没有定义加法。

Exercise 3.27

Assuming txt_size is a function that takes no arguments and returns an int value, which of the following definitions are illegal? Explain why.

unsigned buf_size = 1024;

int ia[buf_size];   // 非法，数组的维度必须是常数。
int ia[4 * 7 - 14]; // 合法。
int ia[txt_size()]; // 非法。
char st[11] = "fundamental";  // 非法，字符串字面值初始化数组会在尾部加一个空字符，空间不够。

Exercise 3.28

What are the values in the following arrays?

string sa[10];  // 空字符串
int ia[10];     // 函数外默认初始化0

int main() {
  string sa2[10];   // 空字符串
  int ia2[10];      // 未定义
}

Exercise 3.29

List some of the drawbacks of using an array instead of a vector.

初始化和赋值不方便。
不够灵活，不能改变大小。
没有迭代器，可能超出范围。
没有基于迭代器的算法，功能不丰富。

Exercise 3.30

Identify the indexing errors in the following code:

constexpr size_t array_size = 10;
int ia[array_size];
for (size_t ix = 1; ix <= array_size; ++ix)
      ia[ix] = ix;

数组下标越界。

Exercise 3.31

Exercise 3.32

Exercise 3.33

What would happen if we did not initialize the scores array in the program on page 104?

值未定义。

Exercise 3.34

Given that p1 and p2 point to elements in the same array, what does the following code do? Are there values of p1 or p2 that make this code illegal?

p1 += p2 - p1;

让p1等于p2，合法。

Exercise 3.35

Exercise 3.36

Exercise 3.37

What does the following program do?

const char ca[] = {'h', 'e', 'l', 'l', 'o'};
const char *cp = ca;
while (*cp) {
    cout << *cp << endl;
    ++cp;
}

定义一个C风格字符串 ca ，把 ca 首元素指针赋值给 cp ，打印数组所有非空字符。

Exercise 3.38

In this section, we noted that it was not only illegal but meaningless to try to add two pointers. Why would adding two pointers be meaningless?

指针相减可以得到它们之间要移动多少，而相加的值不能用来访问指定的对象，所以没有意义。

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