01_C++读书笔记

入门：

void hello() {

    cout << "!!!hello world!!!" << endl;

    int a = 1;
    cout << a << endl;

    int b;
    cout << "enter a number:" << endl;

    cin >> b;
    cout << "xxxxxxxxxxxx: " << b << endl;
}

数据类型：

/**
 * unsigned long:
 * long:
 * unsigned int:
 * int:
 * unsigned short:
 * short:
 * unsigned char:
 * char:
 * bool:
 *
 * C11新增两个类型：
 * unsigned long long:
 * long long
 */
int dataType() {
    unsigned long ul = ULONG_MAX;
    cout << "unsigned long: " << sizeof(ul) << endl;    //unsigned long: 4
    cout << ul << endl; //4294967295

    char a = 'A';
    cout << "A:" << a + 1 << endl;
    cout << a << endl;
    cout.put(a);
    return 0;
}

数组：

/**
 * array
 */
int arrayDemo() {

    int nums[3] = { 2 };

    cout << nums[0] << endl;
    cout << nums << endl;   //0x62ff04
    cout << sizeof(nums) << endl;   //12
    return 0;
}

字符串：

int stringDemo() {

    // C 语言中的字符串 形式1
    char chs01[8] = { 'a', 'b', 'c', 'd', 'e', '2', '3', 'g' };
    char chs02[8] = { '1', '2', '3', '4', '\0' };

    cout << chs01[5] + 0 << endl;
    cout << chs01[6] + 0 << endl;
    cout << chs01[7] + 0 << endl;
    cout << chs01[8] + 0 << endl;
    cout << chs01[9] + 0 << endl;
    cout << chs01[10] + 0 << endl;
    cout << chs01[11] + 0 << endl;
    cout << chs01 << endl;  //abcde23g`�@
    cout << chs02 << endl;  //1234

    // C 语言中的字符串 形式2
    char chs03[8] = { "hello" };//unused variable 'chs03' [-Wunused-variable]
    char chs04[8] { "hello" };

    cout << chs03 << endl;
    cout << chs04 << endl;
    return 0;
}

int stringDemo02() {

    const int Size = 15;
    char name1[Size];
    char name2[Size] = { "HelloWorldwer" };
    char name3[Size];
    char name4[Size];
    //array must be initialized with a brace-enclosed initializer
    //char name2[15] = "HelloWorld"; //编译通过不了
    //char name2[15] = {"HelloWorldwer"};
    //char name3[Size];

    cout << sizeof(name1) << endl;  //获取存储字符串声明的长度
    cout << strlen(name1) << endl;  //strlen获取字符串实际的长度 10
    cout << strlen(name2) << endl;  //13
    cout << strlen(name3) << endl;  //0
    cout << strlen(name4) << endl;  //7

    //输出内容
    cout << name1 << endl;  //?_v\r\n乢v?�@
    cout << name2 << endl;  // HelloWorldwer
    cout << name3 << endl;  //没内容
    cout << name4 << endl;  //孒?*?�@

    cout << &name1 << endl; //0x62fefd
    cout << &name2 << endl; //0x62feee
    cout << &name3 << endl; //0x62fedf
    cout << &name4 << endl; //0x62fed0
    //cout << strlen(name3) << endl;

    //cout << sizeof(name2) << endl;
    //cout << strlen(name2) << endl;

    cout << "----------------------------" << endl;
    cout << "前--第6个位置的元素：" << name1[5] + 0 << endl;
    cout << "前--第7个位置的元素：" << name1[6] + 0 << endl;
    cout << "前--第8个位置的元素：" << name1[7] + 0 << endl;
    //给name1赋值，会修改赋值字符串紧跟的那个字符的值
    //赋值前，需要结束的位置的元素值并不是\0
    //赋值前，需要结束的位置的元素值变为\0
    //但是我们并没有输入\0,我们输入的回车换行
    //C++ 会将 空白，制表符，换行符作为字符串输入的结束

    cout << "enter name1:" << endl;
    cin >> name1;
    cout << strlen(name1) << endl;
    cout << name1 << endl;
    cout << "后--第6个位置的元素：" << name1[5] + 0 << endl;
    cout << "后--第7个位置的元素：" << name1[6] + 0 << endl;
    cout << "后--第8个位置的元素：" << name1[7] + 0 << endl;
    // C 语言中的字符串
    //char chs01[8]={'a','b','c','d','e','2','3','g'};
    //char chs02[8]={'1','2','3','4','\0'};

    return 0;
}

//面向行的输入getline() -- 换行符不在输入队列中
int string_demo03() {
    const int Size = 15;

    char name1[Size];
    char name2[Size];

    cout << "enter your name1: " << endl;
    cin.getline(name1, Size);
    cout << "name1: " << name1 << endl;

    cout << "enter your name2: " << endl;
    cin.getline(name2, Size);
    cout << "name2: " << name2 << endl;

    return 0;
}

//面向行的输入get() -- 换行符仍旧在输入队列中
void string_demo04() {
    const int Size = 15;

    char name1[Size];
    char name2[Size];

    cout << "enter your name1: " << endl;
    cin.get(name1, Size).get();
    cout << "name1: " << name1 << endl;

    cout << "enter your name2: " << endl;
    cin.get(name2, Size).get();
    cout << "name2: " << name2 << endl;

    //return 0;
}

/**
 * 混合输入的问题：
 */
void string_demo05() {

    const int Size = 15;

    int age;
    char name2[Size];

    cout << "enter your age: " << endl;
    cin >> age;
    cin.get();
    cout << "age: " << age << endl;

    cout << "enter your name2: " << endl;
    cin.getline(name2, Size);
    cout << "name2: " << name2 << endl;

}

/**
 * string 类的简介
 */
void string_demo06() {
    //1. C 风格给字符串对象赋值
    string s1 = "hello";

    string s2;
    //2. 使用cin接收字符串对象的值
    cout << "请输入s2字符串的值：" << endl;
    cin >> s2;
    //3. 使用cout输出字符串的值
    cout << s2 << endl;

    //4. 访问字符串中的元素,可以类似字符数组访问
    cout << s2[1] << endl;
    //5. 赋值
    string s3 = s2;
    cout << s3 << endl;
    //6. 拼接
    string s4 = s1+s2;
    cout << s4 << endl;
    //7. 追加
    s1 += s2;
    cout << s1 << endl;

    //C 风格 字符串操作
    //8. strcpy(charr1,charr2);//copy charr2 to charr1
    char arr1[18] = {"HelloWorld"};
    cout << arr1 << endl;
    char arr2[5];
    strcpy(arr2,arr1);//疑问？？
    cout << arr2 << endl;//HelloWorld,超过arr2的长度就发生意想不到的情况。
    cout << "xxxxxxxxxxxxxxxxxxxx: " << arr1 << endl;//World
    //9. strcat(charr1,charr2);//append content of charr2 to charr1
    char arr3[18] = {"333"};
    char arr4[18] = {"HelloWorld"};
    strcat(arr4,arr3);
    cout << arr4 << endl;
}

结构体：

#include <iostream>
//#include <climits>
//#include <cstring>

struct student {

    char name[20];
    int age;
    double score;
    //使用字符串作为成员变量
    std::string addr;
};

/**
 * 枚举主要用来定义相关的符号常量，而不是用来定义新的类型
 */
enum spectrum {red,orange,yellow,green,blue,violet,indigo};

// 如果只使用符号常量，可以省略枚举名字
enum {red1,orange1,yellow1,green1,blue1,violet1,indigo1};

//指定枚举元素对应的数值
enum spectrum2 {red2=3,orange2=6,yellow2=9};

void mail();

int main2() {
    using namespace std;
    spectrum band = red;
    //spectrum band2 = kkk;//invalid conversion from 'int' to 'spectrum' [-fpermissive]

    //band = red+blue;//invalid conversion from 'int' to 'spectrum' [-fpermissive]
    int a = red2;
    cout << a << endl;


    struct person {

        char name[20];
        int age;
        double score;
        string addr;
    };

    /**
     * 声明一个结构体，struct 关键字在C++中可以省略，C语言不能省略
     */
    struct student stu1 = { "hello", 23, 34.5 };

    person p = { "hello", 23, 34.5 };

    cout << stu1.age << stu1.name << stu1.score << endl;

    cout << stu1.name[1] << endl;
    return 0;
}

void mail() {
    struct student stu1 = { "hello", 23, 34.5 };
    //person p = {"hello",23,34.5};//Type 'person' could not be resolved
}

指针：

/*
 * pointer_demo.cpp
 *
 *  Created on: 2019年5月19日
 *      Author: guo20
 */
#include <iostream>


/**
 * 计算机程序在存储数据的时候必须跟踪的3中基本属性：
 * 1. 信息存储在何处
 * 2. 存储的值是多少
 * 3. 存储的信息是什么类型
 *
 * 如何实现？
 * 1. 定义一个变量，声明出类型和符号名，让程序分配内存，并在内存中跟踪该内存单元。
 * 2. 指针：指针是一个变量，是存储了变量的地址，而不是值。
 *
 * 指针策略：内存管理编程理念的核心
 * 指针：用于存储值的地址，因此：指针名表示的是地址， * 指针名可以得到该地址的处存储的值
 */
int main3() {

    using namespace std;

    int num1 = 3;
    double num2 = 2.3;

    //获取变量的地址
    cout << &num1 << endl;
    cout << &num2 << endl;

    return 0;
}

#include <iostream>
using namespace std;


void string_demo();
void getAddress();
void pointer01();
void pointer02();
void pointer03();
void pointer04();
void pointer05();


struct student
{
    char name[20];
    float weight;
    int age;
};


int main1() {

    cout << (3 < 5) << endl;//1 true
    cout << (3 > 5) << endl;//0 false
    
    cout.setf(ios_base::boolalpha);//设置标记
    cout << (3 < 5) << endl;//true
    cout << (3 > 5) << endl;//false

    return 0;
}
void pointer05(){
    student stu01,stu02,stu03;

    //创建指针数组
    //stus 是一个指针数组，stus[1] 就是一个指针
    const student * stus[3] = {&stu01,&stu02,&stu03};

    cout << stus[1] -> age << endl;

    //可以创建上述数组的指针
    //stus 是一个数组的名称，它是第一个元素的地址。
    //但是其第一个元素为指针，因此 ppa也是一个指针
    // 指向一个 const student 的指针。这种声明很容易出错。
    const student ** ppa = stus;
}
void pointer04(){
    struct student stu = {"aa",34.5,21};

    cout << "name:" << stu.name << ",age:" << stu.age << ",weight:" << stu.weight << endl;
    student * p_stu = new student;
    p_stu -> weight = 56.7;
    p_stu -> age = 56;

    cout << "enter p_stu name: " << endl;
    cin.get(p_stu->name,20);
    cout << "name:" << (* p_stu).name << endl;//expression must be a modifiable lvalue
    cout << "weight:" << p_stu -> weight << endl;
    cout << "age:" << p_stu -> age << endl;
}



void pointer03(){

    int * pn = new int[10];
    pn[0] = 1;
    pn[1] = 2;
    pn[2] = 3;

    cout << sizeof(pn) << endl;//4

    cout << pn[0] << endl;
    cout << pn[1] << endl;
    cout << &pn[1] << endl;
    cout << pn[2] << endl;

    cout << pn << endl;
    //将指针变量加1后，其增加的值等于指向的类型占用的字节数
    //pn[1] 获取的第二个元素的值，可以看成是  * (pn+1)
    // 这意味：先计算数组第二个元素的地址，然后找到存储在那里的值。
    // 所以： pn[1] 等价于 * (pn+1)
    // 数组的通用写法： arrayname[i] 等价于 *(arrayname+i)
    // 指针的通用写法： pointername[i] 等价于 *(pointername+i)

    //区别1： 指针可以写 pn = pn+1,数组不能这么写
    //区别2：sizeof (数组) 得到的数组的长度, sizeof(指针) 得到的指针的长度。
    pn = pn + 1;
    cout << pn << endl;
    cout << pn[0] << endl;
    pn = pn - 1;

    delete pn;
}


/**
 * 使用new 分配内存
 */
void pointer02(){

    //分配内存，C++提供了检测并处理内存分配失败的工具
    int * pt = new int;
    double * pd = new double;

    cout << pt << endl;
    cout << pd << endl;

    //赋值
    * pt = 3;
    * pd = 3.4;

    cout << *pt << endl;
    cout << *pd << endl;
}


/**
 * 使用指针修改变量的值
 */
void pointer01(){

    using namespace std;
    int updates = 3; //声明一个变量
    int * p_updates; //声明指针指向int类型
    /**
     * 
     * int* 是指向int类型的指针
     * */
    p_updates = &updates; //将updates的地址保存p_updates
    //p_updates 保存了 updates 的地址，可以说：p_updates 指向了 updates

    //输出两个的值
    cout << "Value: updates = " << updates << endl;//Value: updates = 3
    cout << "Value: * p_updates = " << *p_updates << endl;//Value: * p_updates = 3
    

    //输出两个地址
    cout << "Value: &updates = " << &updates << endl;//Value: &updates = 0x61ff08
    cout << "Value: p_updates = " << p_updates << endl;//Value: p_updates = 0x61ff08

    //使用指针修改变量的值

    * p_updates = *p_updates + 1;
    cout << "Value: updates = " << updates << endl;//Value: updates = 4
    cout << "Value: * p_updates = " << *p_updates << endl;//Value: * p_updates = 4
}


//获取变量的地址
void getAddress(){
        
    using namespace std;

    int num1 = 3;
    double num2 = 2.3;

    //获取变量的地址
    cout << &num1 << endl;
    cout << &num2 << endl;
}

#include<iostream>
using namespace std;

struct student {
    int age;
};

int main4() {
    student stu01, stu02, stu03;
    stu01.age = 1998;

    student * pa = &stu02;
    pa->age = 2003;

    student * pa02 = &stu03;
    pa02->age = 1200;

    student stus[3];
    stus[0].age = 1;
    stus[1].age = 2;
    stus[2].age = 3;

    cout << stus->age << endl;
    cout << (stus + 1)->age << endl;
    cout << (stus + 2)->age << endl;

    stu01.age = 1998;
    //创建指针数组
    const student * arp[3] = { &stu01, &stu02, &stu03 };

    cout << arp[1]->age << endl;
    cout << arp[2]->age << endl;
    cout << arp[0]->age << endl;
    //创建指针,ppa 保存了arp的首元素地址
    const student ** ppa = arp;

    cout << (*ppa)->age << endl;
    cout << (*(ppa+1))->age << endl;
    cout << (*(ppa+2))->age << endl;

    //auto ppb = arp;//C++ automatic type deduction

    //or else use const student ** ppb = arp;

    return 0;
}

循环：

/*
 * loop_demo.cpp
 *
 *  Created on: 2019年5月21日
 *      Author: guo20
 */

#include <iostream>
#include <cstring>

using namespace std;

const int ArSize = 16;

void loop02();

int main_loop(){

    loop02();
    return 0;
}


void loop02(){
    string word = "hello";

    //如果两个字符串相等，则下面的结果为 true
    bool b = strcmp("aa","aa") == 0;

    cout.setf(ios_base::boolalpha);
    cout << strcmp("","") << endl;
    cout << b << endl;//false

    //cout << "enter a word: " << endl;
    //cin >> word;
    /*for (unsigned int i = 0; i < word.size(); i++)
    {
        cout << word[i];
    }
*/
}

if:

#include <iostream>
#include <fstream>
#include <cctype>
void if_demo() {
    while (true) {

        cout << "enter a char letter: " << endl;
        char a;
        //cin >> a;

        cin.get(a);

        if (isalpha(a)) {
            cout << "字母" << endl;
        } else if (isdigit(a)) {
            cout << "数字" << endl;
        } else if (ispunct(a)) {
            cout << "punct" << endl;
        } else if (isspace(a)) {
            cout << "space" << endl;
        } else {

            cout << "other" << endl;
            exit(EXIT_FAILURE);
        }
    }
}