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引言

记录从零开始学习C++的过程。

记录

2024-09-06

无符号和有符号数字

整型

有符号则表示可以为负数，无符号则从0开始。

signed int num1 = 30;//有符号整型
int num2 = -30;//有符号整形，signed可省略
unsigned int num3 = 30;//无符号整形，必须大于0

//无符号变量快捷写法
u_int num4 = 1;
u_short num5 = 2;
u_long num6 = 3;

实型

float,double,long double
实型默认有符号，即无signed或unsigned

常量可以具有后缀，如0LL
U : 表示无符号整形(unsigned)
L : 表示long类型或long double 类型
LL : 表示long long 类型
UL：表示unsigned long 类型
ULL: 表示 unsigned long long 类型
F ：表示float 类型
注：整数类型默认int，小数类型默认double

char类型

char类型本质上是数字，即在内存中实际上存储的是数字
通过ASCII码表作为对照，字符 -> 数字存入，数字 -> 字符使用

转义字符

常用的
\n 换行符
\t 制表符，用于对齐
\' 打印'
\" 打印"
\ 打印\

2024-09-07

字符串

//C语言风格字符串
char str1[] = "你好"; //字符数组形式字符串
char *str2 = "你好"; //指针形式字符串

//C++语言风格字符串
string str3 = "你好";

字符串拼接

使用+号拼接，如果存在int型变量，需要用to_string()函数转化为字符串

数据输入 cin

int a; //声明a
cin >> a; //输入传给a

string name;
cout << "请输入姓名：" << endl;
cin >> name;

int age;
cout << "请输入年龄：" << endl;
cin >> age;

算术运算符

+,-,*,/,%(取余),++,--

a = 2;
b = ++a;//先运算后赋值
// a = 3 , b = 3

a = 2;
b = a++;//先赋值后运算
// a = 3 , b = 2

比较运算符

c语言风格字符串在用比较运算符比较时，比较的是内存地址，因此需要用strcmp(s1,s2)函数进行比较

#include "cstring"
int result = strcmp(s1,s2);//-1 s1<s2 ,0 s1=s2,1 s1>s2

while循环

案例1：输出1-100的和

int i = 1;
int sum = 0;
while (i <= 100) {
sum += i;
i++;
}
cout << "1-100的和为：" << sum << endl;

案例2：猜一个100以内的数字

#include "iostream"
#include "random"
using namespace std;

int getRandom(int x, int y) {
    mt19937 engine(std::random_device{}());
    uniform_int_distribution<int> distribution(x, y);
    int randomNumber = distribution(engine);
    return randomNumber;
}

int main() {
    int randomnum = getRandom(1,100);
    int input_num;
    int guess_times = 0;
    cout << "请输入一个1到100的数字" << endl;
    cin >> input_num;
    while (!(randomnum == input_num)) {
        if (randomnum > input_num) {
            cout << "小了" << endl;
        }
        else {
            cout << "大了" << endl;
        }
        cout << "请重新输入" << endl;
        cin >> input_num;
        guess_times++;
    }
    cout << "猜中了！你一共猜了"<< guess_times << "次" << endl;
    return 0;
}

案例3：九九乘法表

// 九九乘法表
int row = 1;
while (row<=9) {
    int col = 1;
    while (col <= row) {
        cout << col << "×" << row << "=" << row * col << "\t";
    col++;
    }
    cout << endl;
    row++;
}

do while循环

案例1：猜一个100以内的数字

#include "iostream"
#include "random"
using namespace std;

int getRandom(int x, int y) {
    mt19937 engine(std::random_device{}());
    uniform_int_distribution<int> distribution(x, y);
    int randomNumber = distribution(engine);
    return randomNumber;
}

int main() {
    int randomnum = getRandom(1,100);
    cout << randomnum << endl;
    int input_num;
    int guess_times = 0;
    cout << "请输入一个1到100的数字" << endl;
    do {
        guess_times++;
        cin >> input_num;
        if (randomnum > input_num) {
            cout << "小了" << endl;
        }
        else if (randomnum < input_num){
            cout << "大了" << endl;
        }
        else {
            cout << "猜中了" << endl;
            break;
        }
        cout << "请重新输入" << endl;
    } while (randomnum != input_num);
    cout << "你一共猜了"<< guess_times << "次" << endl;
    return 0;
}

for循环

案例1：发工资

int balance = 10000;
for (int i = 1; (i <= 20) && (balance>0); i++) {
    int rank = getRandom(1,10);
    if (rank <5) {
        cout << "员工" << i << "，绩效分" << rank << "，低于5，不发工资，下一位" << endl;
    }
    else {
        balance -= 1000;
        cout << "向员工" << i << "发放工资1000元，账面余额还剩" << balance << "元" << endl;
    }
}

2024-09-09

数组遍历for循环

//普通写法
int arr[] = {1,2,3,4,5};
for(int i;i<sizeof(arr)/sizeof(arr[0]);i++){
    //code
}

//高级写法
int arr[] = {1,2,3,4,5};
for(int i: arr){
    //code
}

2024-09-10

数组遍历

#include "iostream"
using namespace std;

int main() {
    int v[2][2] = {
        {1,2},{1,2}
    };

    for (int i = 0; i < sizeof(v) / sizeof(v[0]); i++) {
        for (int j = 0; j < sizeof(v[0]) / sizeof(v[0][0]); j++) {
            cout << v[i][j] << endl;
        }
    }
    return 0;
}

指针运算

指针+n或-n，地址加 *类型n**

//int
int num = 1;
int* p = &num;

cout << p << endl;//000000C5EE8FFC24
p++;
cout << p << endl;//000000C5EE8FFC28

//double
double num = 1;
double* p = &num;

cout << p << endl;//000000B361AFF908
p++;
cout << p << endl;//000000B361AFF910

用途

对数组进行操作

int v[] = { 1,2,3 };
int *vp = v;

cout << *vp << endl;//1
vp++;
cout << *vp << endl;//2
vp++;
cout << *vp << endl;//3

//或
int v[] = { 1,2,3 };
int *vp = v;

cout << *(vp) << endl;
cout << *(vp + 1) << endl;
cout << *(vp + 2) << endl;

因为v实际上记录的是v数组中0号元素的地址

动态内存分配

概念：由C++自动分配的内存，称之为（自动）静态内存分配，不会进行内存空间的自动清理。（无垃圾回收机制）只有程序结束或所在作用域结束才会清理。于是我们需要手动管理内存，用完清理。

这里用到了new和delete运算符

//new type
//new type[]
//delete 指针
//delete[] 指针
int *p = new int;
*p = 10;
cout << *p << endl;
delete p;

int* p = new int[5];
p[0] = 1; // 等同于*(p+0)
*p = 1;

p[1] = 3; // 等同于*(p+1)
cout << p[0] << endl;
cout << *(p + 1) << endl;

delete[] p;

用完就删，也就是说在new和delete中写代码。

2024-09-11

数组元素移除

案例：从数组中取出偶数形成新数组

int* pArr = new int[10] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

int* newarr = new int[5];

for (int i = 0; i < 10; i++) {
    if ((pArr[i] % 2) == 0) {
        newarr[(i - 1) / 2] = pArr[i];
    }
}
delete[] pArr;
for (int j = 0; j < 5; j++) {
    cout << "新数组中的元素为：" << newarr[j] << endl;
}
delete[] newarr;

数组元素添加

案例：向数组中添加元素形成新数组

int* pArr = new int[3] {1, 3, 5};

int* newarr = new int[5];
int offset = 0;
for (int i = 0; i < 5; i++) {
    if (i == 1) {
        offset++;
        newarr[i] = 2;
        continue;
    }
    else if (i == 3) {
        offset++;
        newarr[i] = 4;
        continue;
    }
    newarr[i] = pArr[i - offset];
}
delete[] pArr;
for (int j = 0; j < 5; j++) {
    cout << "新数组中的元素为：" << newarr[j] << endl;
}

2024-09-12

常量指针

int num = 10,num2 = 20;

const int * p = &num;//指向const的指针，p的指向可以更改，p指向的内容不可修改

int * const p = &num2;//指向不可变，数据可变

const int * const p = &num1;//指向不可变，数据不可变

应用场景：需要常量的同时也需要动态内存分配的场景

2024-09-13

对数组升序处理

//类似冒泡排序
int* pArr = new int[10] {5, 2, 6, 34, 12, 78, 3, 5, 12, 7};
int* a = new int;
int offset = 9;
int count = 0;
for (int i = 0; i < 9; i++) {
    for (int j = 0; j < offset; j++) {
        count++;
        if (pArr[j] > pArr[j + 1]) {
            *a = pArr[j + 1];
            pArr[j + 1] = pArr[j];
            pArr[j] = *a;
        }
    }
    offset--;
}
cout << "执行了" << count << "次" << endl;//45次
delete a;
for (int i = 0; i < 10; i++) {
    cout << "升序后数组：" << pArr[i] << endl;
}
delete[] pArr;

结构体

案例：录入五个学生的姓名，年龄，地址

struct Student {
    string name;
    int age;
    string address;
};

struct Student* stu = new Student[5];

for (int i = 0; i < 5; i++) {
    cout << "请输入姓名：";
    cin >> stu[i].name;
    cout << endl;
    cout << "请输入年龄：";
    cin >> stu[i].age;
    cout << endl;
    cout << "请输入地址：";
    cin >> stu[i].address;
    cout << endl;
}
for (int i = 0; i < 5; i++) {
    cout <<"姓名："<< stu[i].name << endl;
    cout <<"年龄："<< stu[i].age << endl;
    cout <<"地址："<< stu[i].address << endl;
}
delete[] stu;
for (int i = 0; i < 5; i++) {
    cout << "姓名：" << stu[i].name << endl;
    cout << "年龄：" << stu[i].age << endl;
    cout << "地址：" << stu[i].address << endl;
}

函数

案例1：获取三个数中最小数

int get_min(int a,int b,int c) {
    int min;
    min = a;
    if (a > b) {
        min = b;
        if (b > c) {
            min = c;
        }
    }
    else if (a < b) {
        min = a;
        if (a > c) {
            min = c;
        }
    }
    else if(a==b){
        if (a > c) {
            min = c;
        }
    }
    return min;
}

案例2：找最大最小，返回结构体(函数嵌套调用)

int get_min(int a, int b) {
    int min;
    min = a;
    if (a > b) {
        min = b;
    }
    return min;
}

int get_max(int a, int b) {
    int max;
    max = b;
    if (a > b) {
        max = a;
    }
    return max;
}

struct MinAndMax {
    int min;
    int max;
};

struct MinAndMax get_struct(int a, int b) {
    int min, max;
    int min = get_min(a, b);
    int max = get_max(a, b);
    struct MinAndMax srt = {min,max};
    return srt;
}

int main() {
    int num1, num2;
    struct MinAndMax srt = {};
    cout << "请输入第一个数" << endl;
    cin >> num1;
    cout << "请输入第二个数" << endl;
    cin >> num2;
    srt = get_struct(num1, num2);
    cout << "结构体中最小值为" << srt.min << endl;
    cout << "结构体中最大值为" << srt.max << endl;
    return 0;
}

案例3：银行余额查询，存取款

#include "iostream"
using namespace std;

void query_balance(int * inital_balance,string *name) {

    cout << *name << "，您好，您的余额剩余" << *inital_balance << "元" << endl;
}

void save_money(int* inital_balance, string *name,int* money) {

    *inital_balance += *money;
    cout << name << "，您好，您存款" << *money << "元成功" << endl;
    query_balance(inital_balance, name);
}

void get_money(int* inital_balance, string *name, int* money) {

    *inital_balance -= *money;
    cout << name << "，您好，您取款" << *money << "元成功" << endl;
    query_balance(inital_balance, name);
}

int main() {
    int* inital_balance = new int(5000000);
    string *name = new string;
    int choose;
    int* money = new int;
    cout << "请输入姓名：" << endl;
    cin >> *name;
    while (true) {
        cout << "----------主菜单----------" << endl;
        cout << *name << "，您好，欢迎来到银行ATM。请选择操作：" << endl;
        cout << "查询余额[输入1]" << endl;
        cout << "存款\t[输入2]" << endl;
        cout << "取款\t[输入3]" << endl;
        cout << "退出\t[输入0]" << endl;
        cin >> choose;
        switch (choose) {
        case 1:
            cout << "----------查询余额----------" << endl;
            query_balance(inital_balance,name);
            break;
        case 2:
            cout << "----------存款----------" << endl;
            cout << *name << "，您好，您要存多少元：";
            cin >> *money;
            save_money(inital_balance, name, money);
            break;
        case 3:
            cout << "----------取款----------" << endl;
            cout << *name << "，您好，您要取多少元：";
            cin >> *money;
            get_money(inital_balance, name, money);
            break;
        }
        if (choose == 0) {
            return 0;
        }
    }
    return 0;
}

2024-09-21

引用的本质

//自动转换为int* const ref = &a;
int& ref = a;

2025-03-25

类和对象

struct和class
struct的默认成员权限是public
class的默认成员权限是private

引言

记录