c++ primer（第五版）学习笔记及习题答案代码版（第三章）字符串、向量和数组
笔记较为零散，都是自己不熟悉的知识点。
习题答案至于一个.cc 中，需要演示某一题直接修改 #define NUM**， 如运行3.23题为#define NUM323；
chapter 3
1、
string a4(n, 'c'); //把s4初始化为由连续n个字符c组成的串。
string s5 =string(10,'c'); //拷贝初始化
while(getline(cin, line)) //每次读入一整行，知道达到文件末尾
cout<< line <<endl;
触发getline函数返回的按个换行符实际上被丢弃了，得到的string对象不包含换行符。
string.empty(); //函数返回一个对应的布尔值
string.size(); //返回一个string::size_type类型的值，这是一个unsigned int型
//所以，一条表达式中已经有size()函数就不要再使用int了，避免混用带来问题。
string s3 = s1 + s2; //两个string对象相加
string s4 = "hello" + ","; //包含字面值相加的情况，必须保证+两侧中有一个是string型
2、
为兼容C语言的标准库，C++将这些文件命名为cname。在名为cname的头文件中定义的名字从属于命名空间std,而定义在.h中的头文件则不然。
decltype(s.size()) punct_cnt =0; //punct_cnt的类型和s.size的返回值类型一样。
ispunct(c); //判断标点符号的个数
for(auto &c : s) //对于s中的每个字符（c是引用）
c = toupper(c); //c是一个引用，因此赋值语句将改变c中字符的值。
cout<< s <<endl;
3、
vector是模板而非类型，由vector生成的类型必须包括vector中元素的类型，例如vector<int>
vector<vector<int>>vector对象的又尖括号和其他元素类型之间要添加一个空格。
vector<int>v1{"a", "an", "the"}; //列表初始化
vector<int> vi =10; //错误，必须使用直接初始化的形式执行想来那个大小。
vector<string> v7{10};vector<string> v8{10, "hi"}; //都不是列表初始化，有10个元素的初始化
vector对象（包括string对象）的下标可用于访问已存在的元素，而不能用于添加元素。
string s("string");
if(s.begin() != s.end()){
auto it = s.begin();
*it = toupper(*it); //通过解引用迭代器来获取它所指示的元素。
}
将指向同一容器中元素的两个迭代器相减，结果是两个迭代器的距离。其类型是difference_type,可正可负，是带符号类型的。
4、
char a3[] = "c++";
const char s4[6] ="Daniel"; //错误，没有空间可存放空字符
指针和数组
string nums ={"one","two","three"};
string *p = &nums[0]; //p指向nums的第一个元素
string *p2 = nums; //等价于p2 = &nums[0];
int arr[] ={0,1,2,3,4,5,6,7,8,9};
int *e = &arr[10]; //指向尾元素的下一个元素
for(int *b = arr; b != e; ++b)
cou<<*b <<endl; //输出arr的元素
5、
两个指针相减的结果类型是一种名为ptrdiff_t的标准库类型，和size_t一样，其也是定义在cstddef头文件中的机器相关的类型。ptrdiff_t是带符号的类型。
int ia[] = {0,2,4,5,8};
int *p = &ia[2];
int k = p[-2]; //p[-2]是is[0]表示的那个元素
内置的下标运算符所用索引值不是无符号类型，这与string和vector不同。
6、
char ca[] = {'c', '*', '1'};
cout << strlen(ca)<<endl; //严重错误，C语言风格的字符串函数，ca没有以空字符结尾
string s("hello");
char *str = s; //错误，不能用string对象初始化char*
const char *str =s.c_str(); //正确。如果想一直使用c_str()返回的数组，最好将其拷贝一份
多维数组
int ia[3][4];
int (*p)[4] = ia;
int *ip[4]; //整形指针的数组
int (*ip)[4]; //指向含有4个整数的数组
#include <iostream>
#include <vector>
#include <cstring>
#define NUM343
using namespace std;
string sa[10];
int ia[10];
int main(){
/*3.1*/
#ifdef NUM31
cout<<"参见：http://blog.csdn.net/refuil/article/details/51226530 "
"http://blog.csdn.net/refuil/article/details/51236735"<<endl;
#endif
/*3.2*/
#ifdef NUM32
string line;
string word;
while(getline(cin, line)//一次读入一行，直至遇见文件结束符
cout << line <<endl;
while(cin >> word) //一次读入一个单词，直至遇见文件结束符
cout << word <<endl;
#endif
/*3.3*/
#ifdef NUM33
cout<<"string类型读取并忽略有效字符之前所有的空白字符，然后读取字符直至再次遇到空白字符，读取终止（空白字符仍留在输入流中）"
"getline()函数不忽略开头的空白字符，读取字符直至遇到换行符，读取终止并丢弃换行符。"<<endl;
#endif
/*3.4*/
#ifdef NUM34
string str1, str2;
cout << "Enter two strings: " <<endl;
cin >> str1 >> str2;
if(str1 == str2)
cout << "They are the same."<<endl;
else if(str1 > str2)
cout << "The bigger one is: " << str1 <<endl;
else
cout << "The bigger one is: " << str2 <<endl;
/* 比较size */
string::size_type len1, len2;
len1 = str1.size();
len2 = str2.size();
if(len1 == len2)
cout << "They are the same length."<<endl;
else if(len1 > len2)
cout << "The longer one is: "<<str1<<endl;
else
cout << "The longer one is: "<<str2<<endl;
#endif
/*3.5*/
#ifdef NUM35
string str, sum;
cout << "Enter two strings: " <<endl;
while(cin >> str)
sum += str;
cout<< "The concatenation of string is: "<< sum <<endl;
/* Add the blank*/
cout << "Enter two strings: " <<endl;
while(cin >> str)
sum += " " + str;
cout<< "The concatenation of string is: "<< sum <<endl;
#endif
/*3.6*/
#ifdef NUM36
string str("abcddefg");
for(auto &c : str){
if(!isspace(c))
c = 'X';
}
cout<< str << endl;
#endif
/*3.7*/
#ifdef NUM37
string str("abcddefg");
for(char &c : str){
if(!isspace(c))
c = 'X';
}
cout << str << endl;
#endif
/*3.8*/
#ifdef NUM38
string str("abcddefg");
int index = 0;
while(index !=str.size()){
if(!isspace(str[index]))
str[index] = 'X';
++index;
}
cout<< "while语句: "<< str<<endl;
/* for语句*/
for(decltype(str.size()) index =0; index != str.size();++index){
if(!isspace(str[index]))
str[index] = 'X';
}
cout<< "for语句: " <<str <<endl;
#endif
/*3.9*/
#ifdef NUM39
string s;
cout << s[0] << endl;
cout<<"输出s字符的第一个字符，不合法，因为s没有初始化是空字符串，是s[0]是无效的."<<endl;
#endif
/*3.10*/
#ifdef NUM310
string str, result;
bool has_punct;
cout<<"Enter the string with punctuation: "<<endl;
getline(cin, str);
for(auto &c : str){
if(ispunct(c))
has_punct = true;
else
result += c;
}
if(has_punct)
cout<<"After the remove: "<< result <<endl;
else{
cout<<"No punctuation character in the string" <<endl;
return -1;
}
#endif
/*3.11*/
#ifdef NUM311
cout<<"当且仅当不去改变 c 值时才是合法的，c的类型是const char&; 如果试图改变就是不合法的。"<<endl;
#endif
/*3.12*/
#ifdef NUM312
cout<<"(b)不合法，赋值左右类型不同，svec是string对象的vector对象，ivec是保存vector<int>对象的vector对象. "<<endl;
#endif
/*3.13*/
#ifdef NUM313
cout<<"(a)0个int元素;(b)10个int元素，值都是0;(c)10个int元素，值都是42;(d)1个int型元素，值是10;(e)两个int元素，10和42;(f)10个string元素，值为0;(g)10个hi元素。"<<endl;
#endif
/*3.14*/
#ifdef NUM314
vector<int> vec;
int i;
cout<<"Enter number: "<<endl;
while(cin >> i){
vec.push_back(i);
}
for(auto &c : vec)
cout<< c;
cout<<endl;
#endif
/*3.15*/
#ifdef NUM315
vector<string> vec;
string i;
cout<<"Enter string : "<<endl;
while(cin >> i){
vec.push_back(i);
}
for(auto &c : vec)
cout<< c;
cout<<endl;
#endif
/*3.16*/
#ifdef NUM316
vector<int> v1; // size:0, no values.
cout<<"v1: size is "<<v1.size()<<" ";
for(auto &c : v1)
cout<< c;
cout<<endl;
vector<int> v2(10); // size:10, value:0
cout<<"v2: size is "<<v2.size()<<" ";
for(auto &c : v2)
cout<< c <<" ";
cout<<endl;
vector<int> v3(10, 42); // size:10, value:42
cout<<"v3: size is "<<v3.size()<<" ";
for(auto &c : v3)
cout<< c <<" ";
cout<<endl;
vector<int> v4{10}; // size:1, value:10
cout<<"v4: size is "<<v4.size()<<" ";
for(auto &c : v4)
cout<< c <<" ";
cout<<endl;
vector<int> v5{10, 42}; // size:2, value:10, 42
cout<<"v5: size is "<<v5.size()<<" ";
for(auto &c : v5)
cout<< c <<" ";
cout<<endl;
vector<string> v6{10}; // size:10, value:""
cout<<"v6: size is "<<v6.size()<<" ";
for(auto &c : v6)
cout<< c <<" ";
cout<<endl;
vector<string> v7{10, "hi"}; // size:10, value:"hi"
cout<<"v7: size is "<<v7.size()<<" ";
for(auto &c : v7)
cout<< c <<" ";
cout<<endl;
#endif
/*3.17*/
#ifdef NUM317
string str;
vector<string> vec;
while(cin >> str)
vec.push_back(str);
for(decltype(vec.size()) index = 0; index != vec.size(); ++index){
for(auto &c : vec[index]){
toupper(c);
}
cout<< vec[index] <<endl;
}
#endif
/*3.18*/
#ifdef NUM318
vector<int> ivec;
ivec[0] = 42;
cout<<"不合法，ivec是空的vector，不允许通过下标形式访问任何元素，只能用push_back添加元素."<<endl;
#endif
/*3.19*/
#ifdef NUM319
vector<int> vec1(10,42);
vector<int> vec2{42,42,....};
vector<int> vec3(10);
for(vector<int>::iterator iter = vec.begin(); iter != vec.end(); ++iter)
*iter = 42;
#endif
/*3.20*/
#ifdef NUM320
int val;
vector<int> vec;
cout<< "Enter numbers: " <<endl;
while(cin >> val)
vec.push_back(val);
if(!vec.size()){
cout<<"No elements! " <<endl;
return -1;
}
cout<<"The result has been sumed: "<<endl;
for(vector<int>::size_type index =0; index < vec.size()-1; index = index +2)//这里不能用index != vec.size();因为index是逢2加，可能直接略过size()大小
cout << vec[index] + vec[index+1] <<" ";
cout<< endl;
//program changed
cout<<"头尾元素相加: "<<endl;
vector<int>::size_type first, last;
for(first = 0, last = vec.size()-1; first < last; ++first, --last)
cout<< vec[first] + vec[last] << " ";
cout<<endl;
#endif
/*3.21*/
#ifdef NUM321
/*原理都在3.20中体现*/
int val;
vector<int> vec;
cout<< "Enter the numbers: "<<endl;
while(cin >> val)
vec.push_back(val);
if(!vec.size()){
cout<<"No element! "<<endl;
return -1;
}
cout <<"相邻两个元素相加: "<<endl;
for(vector<int>::iterator iter = vec.begin(); iter < vec.end()-1; ++iter)
cout<< *iter + *(iter+1) <<" ";
cout<<endl;
//program changed
cout<<"头尾元素相加: "<<endl;
vector<int>::iterator first, last;
for(first = vec.begin(), last = vec.end()-1; first < last; ++first, --last)
cout<< *first + *last << " ";
cout<<endl;
if(first == last)
cout<<"The mid element isn't been sumed: "<< *first<<endl;
#endif
/*3.22*/
#ifdef NUM322
string word;
vector<string> text;
while(cin >> word)
text.push_back(word);
vector<string>::iterator it = text.begin();
for(string::iterator iter = (*it).begin(); iter != (*it).end(); ++iter)
*iter = toupper(*iter);
for(;it != text.end(); ++it)
cout<< *it <<endl;
#endif
/*3.23*/
#ifdef NUM323
vector<int> vec(10,1);
for(vector<int>::iterator iter = vec.begin(); iter !=vec.end(); ++iter){
*iter = (*iter) * 2;
cout<< *iter <<" ";
if(iter == vec.end()-1) cout<<endl;
}
#endif
/*3.24*/
#ifdef NUM324
cout<<"见3.21"<<endl;
#endif
/*3.25*/
#ifdef NUM325
vector<unsigned> scores(11,0);
vector<unsigned>::iterator iter = scores.begin();
unsigned grade;
while(cin >> grade){
if(grade <= 100){
iter = iter + (grade/10);
(*iter)++;
iter = scores.begin(); //The iterator must be returned
}
}
for(iter = scores.begin(); iter != scores.end(); ++iter)
cout<< *iter <<" ";
cout<<endl;
#endif
/*3.26*/
#ifdef NUM326
cout<<"begin + end是非法的，因为vector的迭代器并没有定义+运算符,编译器会报错."<<endl;
#endif
/*3.27*/
#ifdef NUM327
cout<<"(a)非法，buf_size是一个变量，不能用于下标取值。"
"(c)非法，txt_size()是函数调用，不是常量表达式。"
"(d)非法，存放这个字符串的数组必须要有12个元素. "<<endl;
#endif
/*3.28*/
#ifdef NUM328
string sa2[10];
int ia2[10];
cout<< sa[0]<<" "<<sa2[0]<< " "<<ia[0]<<" "<<ia2[0]<<endl;
cout<<"sa, sa2默认构造函数将各元素初始化为空字符串;"
"ia在函数体外初始化，默认初始化0; ia2在函数体内初始化，默认初始化不确定."<<endl;
#endif
/*3.29*/
#ifdef NUM329
cout<<"数组长度固定，要扩大容量，只能重新定义更大的数组再讲之前的拷贝进去；"
"数组也没有vector的size/push_back操作，程序相对较复杂。"<<endl;
#endif
/*3.30*/
#ifdef NUM330
cout<<"ix = array_size时数组越界了."<<endl;
#endif
/*3.31*/
#ifdef NUM331
constexpr size_t array_size = 10;
int ia[array_size];
for(size_t ix =0; ix < array_size; ++ix){
ia[ix] = ix;
cout<< ia[ix]<<" ";
}
#endif
/*3.32*/
#ifdef NUM332
constexpr size_t array_size = 10;
int ia1[array_size];
int ia2[array_size];
cout<<"ia1: ";
for(size_t ix =0; ix < array_size; ++ix){
ia1[ix] = ix;
cout<< ia1[ix]<<" ";
}
cout<<endl;
cout<<"ia2: ";
for(size_t ix =0; ix < array_size; ++ix){
ia2[ix] = ia1[ix];
cout<< ia2[ix]<<" ";
}
cout<<endl;
vector<int> vec1(10);
vector<int> vec2(10);
int i = 0;
cout<<"vec1: ";
for(auto &c : vec1){
c = i;
++i;
cout<< c<<" ";
}
cout<<endl;
i = 0;
cout<<"vec2: ";
for(auto &c : vec2){
c = vec1[i];
++i;
cout<<c<<" ";
}
cout<<endl;
#endif
/*3.33*/
#ifdef NUM333
cout<<"如果不初始化，scores就是未定义的,它的元素取值是不确定的."<<endl;
#endif
/*3.34*/
#ifdef NUM334
p1 += p2 - p1;
cout<<"该语句使得p1也指向p2原来所指向的元素，只要p1和p2都是指向同一个数组的元素，该语句总是合法的。"<<endl;
#endif
/*3.35*/
#ifdef NUM335
int arr[] = {1,2,3,4,5};
int *p = arr;
for(int i= 0; i <= 4; ++i){
*(p + i) = 0;
cout<< *p << " ";
}
cout << endl;
#endif
/*3.36*/
#ifdef NUM336
/*For arrays*/
int arr_size = 5;
int arr1[arr_size], arr2[arr_size];
cout << "Enter 5 numbers for array1: " <<endl;
for(size_t i = 0; i < 5; i++)
cin >> arr1[i];
cout << "Enter 5 numbers for array2: " <<endl;
for(size_t i = 0; i < 5; i++)
cin >> arr2[i];
for(size_t i = 0; i !=arr_size; ++i)
if(arr1[i] != arr2[i]){
cout<< "array1 is not same with array2."<<endl;
return 0;//只要存在一个元素不相同直接退出
}
cout<< "array1 is same with array2."<<endl;
/*For vectors*/
vector<int> vec1(5), vec2(5);
cout<< "Enter 5 numbers for vector1: "<<endl;
for(auto &c : vec1)
cin >> c;
cout<< "Enter 5 numbers for vector2: "<<endl;
for(auto &c : vec2)
cin >> c;
for(vector<int>::size_type ivec =0; ivec != vec1.size(); ++ivec)
if(vec1[ivec] != vec2[ivec]){
cout<< "vector1 is not same with vector2."<<endl;
return 0;
}
cout<< "vector1 is same with vector2."<<endl;
#endif
/*3.37*/
#ifdef NUM337
const char ca[] = {'h','e', 'l', 'l', 'o'};
const char *cp = ca;
while(*cp){
cout << *cp <<endl;
++cp;
}
cout<<"混合C风格的字符串类型，在数组末尾往汪有'/0'结束，所以输出的一般会多于5个字符."<<endl;
#endif
/*3.38*/
#ifdef NUM338
cout<<"当两个指针指向头一个数组，相减表示两者之间的距离；相加却很难解释，也是没有定义的，所以没有意义."
#endif
/*3.39*/
#ifdef NUM339
/*For string*/
string str1 = "linuxc++a";
string str2 = "linuxc++b";
if(str1 > str2)
cout<< str1 <<endl;
else
cout<< str2 << endl;
/*For C style char**/
const char* s1 = "linuxc++c";
const char* s2 = "linuxc++d";
if(strcmp(s1, s2) > 0)
cout<< s1 <<endl;
else
cout<< s2 << endl;
#endif
/*3.40*/
#ifdef NUM340
const char* str1 = "linux";
const char* str2 = "c++";
size_t len = strlen(str1) + strlen(str2);
char* str3 = new char[len+1];;
strcpy(str3, str1);
strcat(str3, str2);
cout << "str3: " <<str3<<endl;
#endif
/*3.41*/
#ifdef NUM341
const size_t arr_size = 5;
int arr[arr_size];
cout<< "Enter 5 numbers for array. "<<endl;
for(size_t i =0; i!= arr_size; ++i)
cin >> arr[i];
vector<int> vec(begin(arr), end(arr));//另一种写法vector<int> vec(arr, arr+arr_size)
for(auto &c : arr)
cout << c << " ";
#endif
/*3.42*/
#ifdef NUM342
int val;
vector<int> vec;
cout<< "Enter numbers for vector: " <<endl;
while(cin >> val)
vec.push_back(val);
if(!vec.size()){
cout<<"No elements! " <<endl;
return -1;
}
size_t ix = 0; //C风格数组的类型与vector的元素不一样,ix需要初始化
int *pstr = new int[vec.size()];
for(vector<int>::iterator i = vec.begin(); i != vec.end(); ++i, ++ix)
pstr[ix] = *i;
for(ix =0; ix < vec.size(); ++ix)
cout<< *(pstr+ix) <<" ";
delete []pstr;
#endif
/*3.43*/
#ifdef NUM343
int arr[3][4] ={0,1,2,3,4,5,6,7,8,9,10,11};
/*版本一*/
for(auto *p = begin(arr); p != end(arr); ++p)
for(auto q = begin(*p); q != end(*p); ++q)
cout<< *q <<" ";
cout<<endl;
/*版本一*/
for(int i =0; i < 3; ++i)
for(int j =0; j < 4; ++j)
cout<< arr[i][j]<<" ";
cout<<endl;
/*版本三*/
using int_array = int[4];
for(int_array *p = arr; p != arr+3; ++p)
for(int *q = *p; q != *p+4; ++q)
cout<< *q <<" ";
cout<<endl;
#endif
/*3.44*/
#ifdef NUM344
int arr[3][4] ={0,1,2,3,4,5,6,7,8,9,10,11};
typedef int int_array[4];
for(int_array *p = arr; p != arr+3; ++p)
for(int *q = *p; q != *p+4; ++q)
cout<< *q <<" ";
cout<<endl;
#endif
/*3.45*/
#ifdef NUM345
int arr[3][4] ={0,1,2,3,4,5,6,7,8,9,10,11};
for(auto (&row)[4] : arr)
for(auto (&col) : row)
cout<< col <<" ";
cout<<endl;
#endif
return 0;
}
参考资料：
c++ primer中文版第五版，电子工业出版社。
c++ primer第四版习题解答，人民邮电出版社。