C++ primer 第三章练习答案

标准库的string类型 和 字符串字面值不是一个东西

string.size() 的返回值类型是 string::size_type 

 

3 .2  

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

int main()
{
string word;
while (cin >> word)
cout << word << endl;

return 0;
}

 

 

3.3  string 忽略第一个有效字符前的所有空格，遇到第一个有效字符开始输入， 遇到空格结束读取
getline 遇到空格继续读取，遇到回车结束读取

 

3.4 

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

// 比较两个字符串是否相等 输出结果并且输出较大的字符串
int main()
{
string str1, str2;
cout << "输入字符串1:" << endl;
cin >> str1;
cout << "输入字符串2：" << endl;
cin >> str2;

if (str1 == str2)
cout << "两个字符串相等" << endl;
else
cout << "俩个字符串不相等" << endl;

if (str1 > str2)
cout << "字符串 " << str1 << " 大" << endl;
else
cout << "字符串 " << str2 << " 大" << endl;

system("pause");

return 0;
}

 

3.5

原程序

# include<iostream>
# include<string>

using namespace std;
// ctrl + z 跳出循环
int main()
{
string tmp, answer;
while (cin >> tmp)
answer += tmp;

cout << "最后的字符串结果是：" << answer << endl;

system("pause");
return 0;
}

 

3.5 改

# include<iostream>
# include<string>

using namespace std;
// ctrl + z 跳出循环
int main()
{
string tmp, answer;
while (cin >> tmp)
answer =answer + ' ' + tmp;

cout << "最后的字符串结果是：" << answer << endl;

system("pause");
return 0;
}

 

3.6

# include<iostream>
# include<string>

using namespace std;

int main()
{
string str;
string tmp("x");
cout << "输入字符串:" << endl;
cin >> str;

for (auto &c : str)
c = 'x';
cout << "结果是：" << str<<endl;

system("pause");

return 0;
}

 

3.7 

就是把上面c的类型变成char类型 发现str 不变成x

 

3.8

# include<iostream>
# include<string>

using namespace std;

int main()
{
string str;
string tmp("x");
cout << "输入字符串:" << endl;
cin >> str;
// i 应该用size_type类型
for (int i = 0; i < str.size(); i++)
str[i] = 'x';

/*

while( i <= str.size())
{
str[i] = 'x';
i++;

}

*/

cout << "结果是：" << str << endl;

system("pause");

return 0;
}

 

3.9

不合法，s未定义，s[0]没有值，造成不可预知的错误。

 

3.10

# include<iostream>
# include<string>

using namespace std;

int main()
{
string str;
cout << "请输入包含标点符号的字符串，我会把他们连接起来(必须是英文的标点)：" << endl;
cin >> str;

for (int i = 0; i < str.size(); i++)
{
if (ispunct(str[i]))
{
for (int j = i; j < str.size(); j++)
str[j] = str[j + 1];

}
}

cout << "结果是："<<str << endl;

system("pause");

return 0;
}

 

3.11 

合法，c为char,是个引用

 

3.12

(a) 正确 ivec是一个 vector<int>类型的 vector

(b) 错误 svec不是 是istring类型

(c) 正确

 

3.13

(a) vector<int> v1; //不包含元素

(b) vector<int> v2(10);   //v2包含十个元素每个元素都是0

(c) vector<int> v3(10, 42); //v3包含十个元素，每个元素都是42

(d) vector<int> v4{10};   //v4只有一个元素10

(e) vector<int> v5{10,42}; //v5有两个元素，10，42

(f)  vector<string> v6{10}; //v6有十个元素，每个元素都是空串。 因为会首先尝试列表初始化，发现类型不一致，就会尝试值来构造vector。

(g) vector<string> v7{10, 'hi'}; // v7有十个元素，每个元素都是字符串"hi"。

 

突然觉得加一下题目比较好，以后自己复习的时候就不用翻书了

 

 

// 3.14 编写一段程序，用cin读入一组整数并把它们存入到一个vector对象
# include<iostream>
# include<vector>
using namespace std;

int main()
{
vector<int> num;
cout << "请输入一组整数：" << endl;
int intger;

while (cin >> intger)
num.push_back(intger);

cout << "结果是:" << endl;
for (auto &i : num)
cout << i << " ";
cout << endl;

system("pause");
return 0;
}

 

// 3.15 改写上面程序，不过这一次读入的是字符串
# include<iostream>
# include<vector>
# include<string>
using namespace std;

int main()
{
vector<string> str;
cout << "请输入一组字符串：" << endl;
string tmp;

while (cin >> tmp)
str.push_back(tmp);

cout << "结果是:" << endl;
for (auto &i : str)
cout << i << " ";
cout << endl;

system("pause");
return 0;
}

 

// 3.17 从cin读入一组此并把它们粗入一个vector对象，然后设法把所有词都改写为大写格式。输出改变后的结果，每个词占一行。
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<string> word_s;
    string word;
    cout << "请输入一组单词：";
    while (cin >> word)
        word_s.push_back(word);

    for (auto &c : word_s)
        for (auto &tmp : c)
            tmp = toupper(tmp);

    for (auto &c : word_s)
        cout << c << endl;


    //不知道为什么运行的时候需要ctrl+z 退出两次
    

    system("pause");

    return 0;
}

 

 

3.18

不合法，因为ivec不包含任何元素，所以ivec[0]错误。

改成 vector<int> ivec(10);

 

//3.19           当然第一个好！
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> v1(10, 42);
    vector<int> v2{ 42,42,42,42,42,42,42,42,42,42 };
    vector<int> v3;
    for (int i = 0; i < 10; i++)
        v3.push_back(42);

    cout << "v1:";
    for (auto &c : v1)
        cout << c << " ";
    cout << endl;

    cout << "v2:";
    for (auto &c : v2)
        cout << c << " ";
    cout << endl;

    cout << "v3:";
    for (auto &c : v3)
        cout << c << " ";
    cout << endl;


    system("pause");

    return 0;
}

 

//3.20 读入一组书存入vector对象，输出相邻的两个数的和
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> v1;
    cout << "输入一组整数：";
    int integer;
    while (cin >> integer)
        v1.push_back(integer);


    cout << "结果是:";
    for(int i = 0; i < v1.size()-1; i++)
        cout << v1[i] + v1[i + 1] << " ";


    system("pause");

    return 0;
}

//3.20改 输出第一个和倒数第一个的和  第二个和倒数第二个的和 以此类推
//就不考虑奇数个值时，中值会*2的特殊情况了

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

int main()
{
    vector<int> v1;
    cout << "输入一组整数：";
    int integer;
    while (cin >> integer)
        v1.push_back(integer);


    cout << "结果是:";
    for(int i = 0; i < v1.size()-1; i++)
        cout << v1[i] + v1[v1.size()-i-1] << " ";


    system("pause");

    return 0;
}

//3.21 使用迭代器重做94  其实我也不知道指的是哪道题。。可能我的书有问题吧。。。。
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> v1;
    int num[10] = { 1,2,3,4,5,6,7,8,9,10 };
    int m = 0;
    while (m != 10)
    {
        v1.push_back(num[m]);
        m++;
    }

    
    for (auto it = v1.cbegin(); it != v1.cend(); it++)
    {
        cout << *it << " ";

    }


    system("pause");

    return 0;
}

//3.22 把text全部改为大写 用迭代器
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    
    string str("wofjsang,test");
    for (auto it = str.begin(); it != str.end(); it++)
    {
        *it = toupper(*it);
        cout << *it;
    }


    cout << endl;



    system("pause");

    return 0;
}

 

//3.22 把text全部改为大写 用迭代器
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> t{ 1,3,4,5,2,7,8,5,6,10 };

    for (auto i = t.begin(); i != t.end(); i++)
    {
        *i *= *i;
    }
    
    for (auto &c : t)
    {
        cout << c << " ";
    }

     
    cout << endl;
    system("pause");

    return 0;
}

 

//3.23 创建含有十个整数的vector对象，然后使用迭代器将所有元素的值都变成原来的两倍。输出vector对象检测是否正确。
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> t{ 1,3,4,5,2,7,8,5,6,10 };

    for (auto i = t.begin(); i != t.end(); i++)
    {
        *i *= *i;

    }

    for (auto &c : t)
        cout << c << " ";


    
    
     
    cout << endl;
    system("pause");

    return 0;
}

 

//3.24 使用迭代器重做3.20  读入一组数 输出相邻两个和 改输出第一个数，最后一个数的和，第二个和倒数第二个 以此类推
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> continer;
    int tmp;
    // 书上说用迭代器遍历的时候不能进行增删操作，不过先定义了迭代器，只有循环输入应该没关系。
    

    cout << "输入一组整数:";
    while (cin >> tmp)
        continer.push_back(tmp);

    cout << "相邻之和：";
    for (auto t1 = continer.begin(); t1 < continer.end() - 1; t1++)
    {
        cout << *t1 + (*t1+1) << " ";
        
    }
    cout << endl;
    cout << "首尾相加：";
    for (auto t1 = continer.begin(),t2 = continer.end()-1; t1 <= t2; t1++, t2--)
    {
        if (t1 == t2)
            cout << *t1;
        else
            cout << *t1 + *t2 << " ";
        

    }
    
     
    cout << endl;
    system("pause");

    return 0;
}

 

//3.25 划分分数段
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{
    vector<int> continer (11);
    int tmp;
    // 书上说用迭代器遍历的时候不能进行增删操作，不过先定义了迭代器，只有循环输入应该没关系。
    

    cout << "输入一组分数整数:";
    

    while (cin >> tmp)
    {
        auto t = continer.begin();
        int a = tmp / 10;
        *(t + a) += 1;




    }
    
    for (auto t = continer.begin(); t < continer.end(); t++)
        cout << *t << " ";

    cout << endl;
    system("pause");

    return 0;
}

3.26 因为两个迭代器 beg 和 end 不能直接相加。

3.27 

（c) 如果txt_size()是一个constexpr 就是正确的

  (d) 错误，空间不够

 

3.28

sa 为空

ia 为10个为0的int

sa2 数组为空。 
ia2 数组含有10个0的int。

 

3.29 

大小确定 不便捷

 

 

3.30 ix<= array_size 越界

 

//3.31
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{    
    int a[10];
    for (int i = 0; i < 10; i++)
    {
        a[i] = i;
        cout << i << " ";

    }
    

    cout << endl;
    system("pause");

    return 0;
}

 

//3.32
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{    
    constexpr size_t array_size = 10;
    vector<int> a(array_size);

    for (int i = 0; i < array_size; i++)
        a[i] = i;

    vector<int> b = a;

    for (auto &t : b)
        cout << t << " ";

    

    cout << endl;
    system("pause");

    return 0;
}

3.33 不初始化的话 这个数组是未定义的， 不能从0开始计数。

3.34 p1指向p2所指的元素 当p1 为尾后指针时错误

 

//3.35
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{    
    int a[5] = { 1,2,3,4,5 };
    int *p = &a[0];
    
    for (int i = 0; i < 5; i++)
    {
        *p = 0;
        p++;
    }

    for (int i = 0; i < 5; i++)
    {
        cout << a[i] << " ";
    }

    cout << endl;
    system("pause");

    return 0;
}

 

 

3.36 数组先比长度，再逐个值比较， vector 直接用==比较。

//3.37 因为这个char数组不是以 /0结尾，所以下面while循环的时候会一直向下寻找下去，直到遇到0为止,所以会输出hello后 很多空格  换行符
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

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



    

    cout << endl;
    system("pause");

    return 0;
}

3.38 两个指针的地址相加，指向了一个内存地址，可是这个内存地址上没有值，所以没有意义。

 

//3.39 因为这个char数组不是以 /0结尾，所以下面while循环的时候会一直向下寻找下去，直到遇到0为止,所以会输出hello后 很多空格  换行符
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
using namespace std;

int main()
{    
    char ia[] = "sup";
    char iaa[] = "suP";
    if (strcmp(ia, iaa) > 0)
        cout << "ia da" << endl;
    else if (strcmp(ia, iaa) < 0)
        cout << "iaa da" << endl;
    else
        cout << "dou da" << endl;
    string ai("sup");
    string aii("suP");
    if (ai > aii)
        cout << "ai da";
    else if (ai < aii)
        cout << "aii da";
    else
        cout << "dou da";
    
    system("pause");

    return 0;
}

//3.40 visual stdio 2015 里面 不让用strcat 和 strcpy函数，报错不安全 ，用strcpy_s,和 strcat_s报错说空间不够，str这个数组不是空的，所以以后C++ 少用C语言的字符串风格。这个例子在dev_c++ 编译通过。


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

int main()
{
    char str1[] = { 'h', 'e','l','l','o' };
    char str2[] = { 'a','b','c','\0' };

    char str[10] = {};

    strcat(str1, str2);
    strcpy(str, str1);
    char *p = str;

    cout << str;
    system("pause");

    return 0;
}

 

//3.41 使用整数数组初始化vector int对象
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
# include<cstring>
using namespace std;

int main()
{
    int a[5] = { 1,2,3,4,5 };

    vector<int> t(begin(a), end(a));

    for (auto &c : t)
        cout << c << " ";

    cout << endl;


    system("pause");

    return 0;
}

//3.42 将含有整型元素的vector拷贝给整形数组
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
# include<cstring>
using namespace std;

int main()
{
    vector<int> num = { 1,2,3,4,5 };
    int a[6];

    for (int i = 0; i < num.size(); i++)
    {
        a[i] = num[i];
        cout << a[i] << " ";

    }
    

    cout << endl;
    system("pause");

    return 0;
}

//3.43
# include<iostream>
# include<string>
# include<vector>
# include<cctype>
# include<cstring>
using namespace std;

int main()
{
    int ia[3][4] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
    for ( int(&p)[4] : ia)
        for (int &q : p)
            cout << q << " ";
    cout << endl;
    
    for (size_t i = 0; i != 3; i++)
        for (size_t j = 0; j != 4 ; j++)
            cout << ia[i][j] << " ";
    cout << endl;

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

    
    

    cout << endl;
    system("pause");

    return 0;
}

//3.44
#include <iostream>
#include <string>
using namespace std;

int main()
{
    int ia[3][4] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
    using int_array = int[4];
    for (int_array& p : ia)
        for (int q : p) cout << q << " ";
    cout << endl;

    for (size_t i = 0; i != 3; ++i)
        for (size_t j = 0; j != 4; ++j) cout << ia[i][j] << " ";
    cout << endl;

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

    system("pause");
    return 0;
}

//3.45
#include <iostream>
#include <string>
using namespace std;

int main()
{
    int ia[3][4] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
    using int_array = int[4];
    for (auto& p : ia)
        for (int q : p) cout << q << " ";
    cout << endl;

    for (auto i = 0; i != 3; ++i)
        for (size_t j = 0; j != 4; ++j) cout << ia[i][j] << " ";
    cout << endl;

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

    system("pause");
    return 0;
}