前言

最近被拉到导师公司实习，闲来无事学习一下cpp。大学课程讲过基础的一点cpp语法，晃过几年，全还给老师了。这次拿《cpp primer》(第五版)慢慢补一下基础，为了防止遗忘，将一些有意义的课后练习做一些简单地记录，也供大家做一些参考，因为本人能力与精力有限，题解或有部分错误，恳请各位指正。

第三章 字符串、向量和数组练习

pratice 3.12

(a) 正确
(b) 错误，svec是string的vector, 但是ivec是int型的vector
? 正确

pratice 3.13

(a) 0
(b) 10 0
? 10 42
(d) 1 10
(e) 2 {10, 42}
(f) 10 “”*10
(g) 10 “hi”*10

pratice 3.14

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int num, temp;
    vector<int> ivec;
    cin >> num;
    for(int i=0;i<num;i++){
        cin >> temp;
        ivec.push_back(temp);
    }
    cout << sizeof(ivec) << endl;
    return 0;
}

pratice 3.15

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int num;
    string temp;
    vector<string> ivec;
    cin >> num;
    for(int i=0;i<num;i++){
        cin >> temp;
        ivec.push_back(temp);
    }
    cout << ivec.size() << endl;
    return 0;
}

pratice 3.16

#include<iostream>
#include<vector>
using namespace std;
int main(){
    vector<int> val(10,42);
    for(auto x:val)
        cout << x << endl;
    return 0;
}

pratice 3.17

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main(){
    int val;
    cin >> val;
    string temp;
    vector<string> s;
    for(int i=0;i<val;i++){
        cin >> temp;
        for(auto &c:temp)
            c = toupper(c);
        s.push_back(temp);
    }
    for(auto word:s)
        cout << word << endl;
    return 0;
}

pratice 3.18

不合法，需要事先对向量进行初始化，修改为以下代码

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main(){
    int val;
    cin >> val;
    string temp;
    vector<string> s;
    for(int i=0;i<val;i++){
        cin >> temp;
        for(auto &c:temp)
            c = toupper(c);
        s.push_back(temp);
    }
    for(auto word:s)
        cout << word << endl;
    return 0;
}

pratice 3.19

vector<int> val(10,42);

vector<int> val(42,42,42,42,42,42,42,42,42,42);

vector<int> val2(val);

第一种方法定义最为简单

pratice 3.20

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int num, temp;
    cin >> num;
    vector<int> ivec;
    for(int i=0;i<num;i++){
        cin >> temp;
        ivec.push_back(temp);
    }
    // 输出相邻整数的和
    for(int i=1;i<num;i++){
        cout << ivec[i-1] + ivec[i] << " ";
    }
    cout << endl;
    // 输出头尾整数的和
    for(int i=0;i<num/2;i++){
        cout << ivec[i] + ivec[num-i-1] << " ";
    }
    cout << endl;

    return 0;
}

pratice 3.21

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int num, temp;
    vector<int> ivec;
    cin >> num;
    for(int i=0;i<num;i++){
        cin >> temp;
        ivec.push_back(temp);
    }
    for(auto it=ivec.begin(); it != ivec.end();it++){
        cout << *it << " ";
    }
    return 0;
}

pratice 3.22

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main(){
    vector<string> text = {"madao", "","is","mp"};
    for(auto it = text.begin(); it != text.end() && !it->empty();++it){
        for(auto &ch : *it)
            ch = toupper(ch);
    }

    for(auto it = text.begin();it != text.end();it++)
        cout << *it << " ";
    return 0;
}

pratice 3.23

#include<iostream>
#include<vector>
using namespace std;
int main(){
    vector<int> ivec;
    for(int i=0;i<10;i++)
        ivec.push_back(i);

    for(auto it = ivec.begin(); it != ivec.end(); it++){
        *it = 2*(*it);
        cout << *it << " ";
    }
    return 0;
}

pratice 3.24

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int num, temp;
    cin >> num;
    vector<int> ivec;
    for(int i=0;i<num;i++){
        cin >> temp;
        ivec.push_back(temp);
    }
    // 输出相邻整数的和
    for(auto it = ivec.begin();it!=ivec.end()-1;it++)
        cout << *it + *(it+1) << " ";

    cout << endl;
    // 输出头尾整数的和
    for(auto it = ivec.begin(), it2 = ivec.end()-1;it<it2;it++, it2--)
        cout << *it + *it2 << " ";
    cout << endl;

    return 0;
}

pratice 3.25

#include<iostream>
#include<vector>
using namespace std;
int main(){
    unsigned grade;
    vector<unsigned> scores(11,0);
    auto it = scores.begin();
    while(cin >> grade) {
        if (grade <= 100)
            *(it+grade/10)++;
    }
    for(;it!=scores.end();it++)
        cout << *it << " ";
    return 0;
}

pratice 3.26

迭代器是相对位置，所以需要加上begin()对应的起始位置

pratice 3.27

(d) 非法，因为其"fundamental"有11个字符，包含最后的结束符，需要至少12个字符大小的char数组

pratice 3.28

null

pratice 3.29

• 数组定义需要事先确定维度，不够灵活
• 数组的大小进过定义后，就不可修改

pratice 3.30

数组的指针从0开始

pratice 3.31

#include<iostream>
using namespace std;
int main(){
    int num[10];
    for(int i=0;i<10;i++)
        num[i] = i;

    for(int i=0;i<10;i++)
        cout << num[i] << " ";
    cout << endl;
    return 0;
}

pratice 3.32

#include<iostream>
#include<vector>
using namespace std;
int main(){
    // 数组实现
    int num[10],num2[10];
    for(int i=0;i<10;i++)
        num[i] = i;
    for(int i=0;i<10;i++){
        num2[i] = num[i];
        cout << num2[i] << " ";
    }
    cout << endl;

    // vector实现
    vector<int> ivec1;
    for(int i=0;i<10;i++)
        ivec1.push_back(i);
    vector<int> ivec2(ivec1);
    for (auto val:ivec2)
        cout << val << " ";
    cout << endl;
    return 0;
}

pratice 3.33

如果不初始化scores数组，其初始值不一定为0，得到的结果不正确

pratice 3.34

p1 = p1 + p2 - p1;
p1 = p2;

即将p2指针赋给p1指针

pratice 3.35

#include<iostream>
using namespace std;
int main(){
    int a[10];
    int *p = a;
    for(int i=0;i<10;i++)
        *(p+i) = 0;
    for(int i=0;i<10;i++)
        cout << *(p+1) << " ";
    return 0;
}

pratice 3.36

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int a1[10]={10,9,8,7,6,5,4,3,2}, a2[10]={10,9,8,7,6,5,4,3,2,1};
    // vector<int>a1,a2;
    for(int i = 0; i < 10; i++){
        if(a1[i] != a2[i]){
            cout << "The two arraies are NOT the same！" << endl;
            return -1;
        }
    }
    cout << "The two arraies are the same!" << endl;
    return 0;
}

pratice 3.37

#include<iostream>
using namespace std;
int main(){
    const char ca[] = {'h', 'e', 'l', 'l', 'o'};
    const char *cp = ca;
    while(*cp){
        cout << *cp << endl;
        ++cp;
    }
    return 0;
}

程序是输出hello字符串，每个字符隔行输出

pratice 3.38

指针用来表示内存地址，指针的数值是该地址也就是0位地址的偏移量，也可以称为坐标。坐标相加得到的新值是没有什么意义的，坐标相减则是距离，坐标加距离则是新坐标，后两者是有意义的。

pratice 3.39

#include<iostream>
#include<cstring>
#include<string>
using namespace std;
int main(){
    string s1 = "hello", s2 = "hello";
    const char cs1[] = "hello", cs2[] = "hello";
    cout << "The two strings are " << ((s1 == s2)? "": "not ") << "the same!" << endl;
    cout << "The two char strings are " << (strcmp(cs1, cs2)==0?"":"not ") << "the same!" << endl;
    return 0;
}

pratice 3.40

#include<iostream>
#include<cstring>
using namespace std;
int main(){
    char s1[] = "Life is like a box of chocolate, ";
    char s2[] = "you never know what you gonna get.-<Forrest.Gump>.";
    char s3[100];   // s3字符串保证空间足够存下s1和s2的所有内容
    strcat(s1,s2);
    strcpy(s3,s1);
    cout << s3 << endl;
    return 0;
}

pratice 3.41

#include<iostream>
#include<vector>
using namespace std;
int main(){
    int a[] = {0, 1, 2, 3, 4, 5};
    vector<int> ivec(begin(a), end(a));
    for(auto i:ivec)
        cout << i << endl;
    return 0;
}

pratice 3.42

#include<iostream>
#include<vector>
using namespace std;
int main(){
    vector<int> ivec{0,1,2,3,4,5};
    int a[10], count = 0;
    for(auto i:ivec){
        a[count++] = i;
    }
    for(int i=0;i<count;i++)
        cout << a[i] << endl;
    return 0;
}

pratice 3.43

#include<iostream>
using namespace std;
int main(){
    int a[2][4] = {0,1,2,3,4,5,6,7};
    // 版本一,范围for语句处理多维数组
    cout << "version 1:" << endl;
    for(int (&row)[4]:a){
        for(int col:row){
            cout << col << " ";
        }
        cout << endl;
    }

    // 版本二，下标运算符
    cout << "version 2:" << endl;
    for(int i=0; i<2;i++){
        for(int j=0; j<4;j++){
            cout << a[i][j];
        }
        cout << endl;
    }

    // 版本三，使用指针遍历
    cout << "version 3:" << endl;
    for(int (*p)[4] = begin(a); p!=end(a);p++){
        for(int *q = begin(*p);q != end(*p);++q)
            cout << *q << " ";
        cout << endl;
    }
}

pratice 3.44

#include<iostream>
using namespace std;
using int_array = int[4];
typedef int int_array[4];
int main(){
    int a[2][4] = {0,1,2,3,4,5,6,7};
    for(int_array *p = a; p!=a+2;p++){
        for(int *q = *p; q!=*p+4;++q)
            cout << *q << ' ';
        cout << endl;
    }
    return 0;
}

pratice 3.45

#include<iostream>
using namespace std;
int main(){
    int a[2][4]={0,1,2,3,4,5,6,7};
    for(auto &p:a){
        for(auto q:p)
            cout << q << ' ';
        cout << endl;
    }
    return 0;
}