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C++语言学习笔记
Published on Tue Nov 19 2019 16:00:00 GMT+0000

[TOC]

I’m refactoring this note into English version. This may spend me lots of time.

But I believe it will be a good form for me to learn English.

Carry on!

C++ Language Studying(Section 1)

Basic C++ Knowledge

Some tiny knowledge points

1B=8bit(B refers byte and b refers bit)

C++ I/O

C++ Sentences

Range for

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for(auto s:str1)
{
    cout<<S<<endl;
}

By using range for, you can process each element in an array or a sequence .

C++ 类

众所周知，支持面向对象编程是C++的一个重要特性，接下来我们来看类。

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class Box
{
   public:
      double length;   // 盒子的长度
      double breadth;  // 盒子的宽度
      double height;   // 盒子的高度
};

带成员函数声明和定义：

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class Box
{
   public:
      double length;   // 长度
      double breadth;  // 宽度
      double height;   // 高度
      // 成员函数声明
      double get(void);
      void set( double len, double bre, double hei );
};
// 成员函数定义
double Box::get(void)
{
    return length * breadth * height;
}
 
void Box::set( double len, double bre, double hei)
{
    length = len;
    breadth = bre;
    height = hei;
}

析构函数：

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class String{
private:
    char* p;
public:
    String(int n);
    ~String();
};
String::~String(){   //析构函数
    delete[] p;
}
String::String(int n){
    p = new char[n];
}

c++继承

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// 基类
class Shape 
{
   public:
      void setWidth(int w)
      {
         width = w;
      }
      void setHeight(int h)
      {
         height = h;
      }
   protected:
      int width;
      int height;
};
 
// 派生类
class Rectangle: public Shape
{
   public:
      int getArea()
      { 
         return (width * height); 
      }
};

//多继承
class <派生类名>:<继承方式1><基类名1>,<继承方式2><基类名2>,…
{
<派生类类体>
};

重载：

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//运算符重载：
Box operator+(const Box& b)
      {
         Box box;
         box.length = this->length + b.length;
         box.breadth = this->breadth + b.breadth;
         box.height = this->height + b.height;
         return box;
      }

//函数重载：
class printData
{
   public:
      void print(int i) {
        cout << "整数为: " << i << endl;
      }
 
      void print(double  f) {
        cout << "浮点数为: " << f << endl;
      }
 
      void print(char c[]) {
        cout << "字符串为: " << c << endl;
      }
};

命名空间

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// 第一个命名空间
namespace first_space{
   void func(){
      cout << "Inside first_space" << endl;
   }
}
// 第二个命名空间
namespace second_space{
   void func(){
      cout << "Inside second_space" << endl;
   }
}
int main ()
{
 
   // 调用第一个命名空间中的函数
   first_space::func();
   
   // 调用第二个命名空间中的函数
   second_space::func(); 
 
   return 0;
}

王氏C++——应付考试内容

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//自由函数与成员函数，运算符重载的不同

#include<bits/stdc++.h>
class complex{
    public:
    complex(int ri = 0, int ii = 0){
        r = ri;
        i = ii;
    }
    int r;
    int i;
    friend complex operator+(const complex &b) ;//友元函数
    //complex operator+(const complex &b) const;  成员函数
};

complex operator+(const complex &a,const complex &b) {
    return complex(a.r+b.r,a.i+b.i);
}

/*
成员函数
complex complex::operator+(const complex &b) const{
    return complex(r+b.r,i+b.i);
}
*/

int main(){
    complex c1(1,1);
    complex c2(2,2);
    complex c3 = c1+c2;
    complex c4 = c2+3;//成员函数无法执行此操作，而友元函数会得出结果c4.r = c2.r+3,c4.r = c2.r;
    return 0;
}

//有关数组一说
float[2] x[100];//这是每个元素为2个float元素为元素的数组的数组。但是是错的，编译不通过。

引用：

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int x = 5;
int &rx = x;
//rx = 7->x = 7

函数：

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datatype func_name(datatype a){
	
}

datatype func_name(datatype &rr){
    rr = 2;
}

datatype func_name(const float &rr){
    rr = 2;//ERROR
}

//example:
int fun(int &i){
    i = 36;
    return i;
}

int main(){
    int i = 3;
    int f = fun(i);
    return 0;
}

//数组名做参数
int calcsum(int x[],int size){
    int sum;
    for (int i = 0; i < size; i++)
    {
        sum+=x[i];
    }
    return sum;
}

int main(){
    int x[2]={1,2};
    int sum = calcsum(x,2);
    return 0;
}

有关类的四个基本函数

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class Clock{
    private:
    int a;
    int b;
    public:
    clock(int a, int b);//构造函数
    clock();//默认构造函数
    clock(int i,int j){
        a = i;
        b = j;
    }
    
    //初始化列表：
    clock(int s, int i):a(s), b(i){};
    
    //析构函数
    ~clock;
    
    //拷贝构造函数
    clock(const clock &c){
        a = c.a;
        b = c.b;
    }
    
    //拷贝赋值函数
    clock& operator=(const clock &c){
        if (&c!= this){   //避免自己拷贝自己的情况
            a = c.a;
            b = c.b;
        }
        return *this;
    }
    
}

常函数：

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class circle{
    private:
    int r;
    public:
    int getR(){
        return r;
    }
    circle(int i){
        r = i;
    }

    float getArea() /*(const)*/{
        return 3.1415926 *r*r;
    }
    float getAreaC() const){
        return 3.1415926 *r*r;
    }
};



int main(){
    const circle c1(1);
    float area = c1.getArea();//错误，不是常函数无法访问const修饰的对象
    float area = c1.getAreaC();//正确
    return 0;
}

继承：

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class circle2:/*(private or protected or public)*/circle{
    ......
}

虚函数：

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#include<iostream>

class Base1{
	public:
    virtual void display() const;
};

void Base1::display() const{
    std::cout<<1<<std::endl;
}

class Base2:public Base1{
    public:
    void display() const ;
};
void Base2::display() const{
    std::cout<<2<<std::endl;
}

void function(Base1 *ptr){//一个指向父类的指针
    ptr->display();
}

int main(){
    Base1 b1;
    Base2 b2;
    function(&b1);//调用 void Base1::display() const
    function(&b2);//调用 void Base2::display() const
}

三种继承方式：父类成员对子类的可见性：

父类访问控制/继承方式： public protected private
public public protected private
protected protected protected private
private private private private

C++ Variable

C++ Variable types:

Type Implication size
bool bool type undefined
char character 8b
wchar_t wide character 16b
char16_t Unicode character 16b
char32_t Unicode character 32b
short short integer 16b
int integer 16b
long long integer 32b
long long long long integer 64b
float single-precision floating point number 6 significant digit
double double-precision floating point number 10 significant digit
long double expand double-precision floating point number 10 significant digit

Use unsigned to state an unsigned variable type, an unsigned variable do not have a sign digit.

Type conversion

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bool a =42;// 0 refers true and the others refer false.
int i =3.14;// the value of i is 3,the fractional digit has been dropped.
double pi =i;//the value of pi is 3
unsigned char c = -1; //the value of c is 255

WARNING: DO NOT USE UNSIGNED TYPE AND SIGNED TYPE VARIABLE AT THE SAME TIME !!!

Reference

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int a=3;
int &num = a;// num is a reference of a
int &num2;//ERROR: reference must be initialized

Pointer

Pointers point to a pointer:

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int a=1024;
int *ptr1 = &a;
int **ptr2 = &ptr1;
cout<<**ptr2<<endl;// output 1024

C++ Standard Library :: begin, end

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int ia[]={1,2,3,4,5,6,7,8,9};
int *beg = begin(ia);//refer a[0]
int *end = end(ia);//refer the next position after the last element of an array

Pointer with custom size:

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int a[2][2];
int *p[2];//NOT THIS: It created a pointer array
int (*p2)[2];//a pointer which can point to an array with 2 ints.
//use decltype or auto:
decltype *p3 = a;

Const

You can use const to make a variable unchangeable.

Top-level-const and Low-level-const:

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int i=0;
int *const p1 = &i;//the value of pointer can not be changed,top-level-const
const int ci =42;//the value of ci can not be changed.
const int *p2 = &ci;//the value of pointer can not be changed

Typedef

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typedef double wages;

Decltype

Use decltype to get a type that a function returns.

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decltype(f()) sum =0;//the type of sum is just the type that f() returns.

Write your own head file

You’d better define your struct and class in a head file .

Data Structure(STL)

Using statement

Before using C++ Standard Library, you can:

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//method 1
std::cout<<"Test"<<std::endl;
//method 2:
using namespace std;
cout<<"123"<<endl;

Using iterator

A sort of intelligence pointer , used for STD .

C++ example:

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#include <bits/stdc++.h>

using namespace std;

int main()
{
    vector<int> vec1;//Statement
    for (int i = 0; i < 5; i++)
    {
        vec1.push_back(i);
    }
    auto it = vec1.begin();//Auto Statement
    vector<int>:: iterator it = vec1.begin();//Standard statement

    cout << *it << endl;
    for (; it != vec1.end(); it++)
    {
        cout << *it << endl;
    }
    
    return 0;
    
}

Operations:

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it = v1.begin();//set v1 refer to the first
*it;//return value
it++;//point to the next
*it = 1234;//change value
it2 = it + 2;//send the address + 2 to another

Stack: a LIFO(Last in First out) data structure

Statement in C++:

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stack<int> stack_name;

Basic operations:

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stack_name.push(data);//push a data into the stack
cout<<stack_name.top();//read the data at top
stack_name.pop();//pop out the data at top

Queue: a FIFO(First in First out) data structure

Statement in C++:

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queue<int> q;

Basic operations:

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q.front();//read the data at the front
q.push();//push a data at the end of the queue
q.pop();//pop out the data at the front
q = queue<int>();//empty the queue

Then, let’s see a sample of using queue.

Cruel torture (AHU77)

Please read the question at bofcOJ

Code:

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#include <bits/stdc++.h>

using namespace std;

int main()
{
    int qty_children = 0, k;
    cin >> qty_children >> k;

    
    int sum = 0;
    queue<int> children;
    for (int i = 1; i <= qty_children; i++)
    {
        children.push(i);
    } //statement queue
    while (sum < qty_children-1)
    {

        for (int i = 0; i < k-1; i++)
        {
            children.push(children.front());//if we do not pull out the line, thus we let this wild kid get to the back.
            children.pop();
        }
        children.pop();//when it comes to pull out the line, this wild kid is over.
        sum++;
    }
    cout << children.front();

    return 0;
}

Using dynamic array with pointer

Code demo:

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int *p = new int[10];//Create an array when running.
delete[] p;//the realease of a dynamic array method is not same with a variable

bitset

A data structure which storages bit.

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bitset<4> bitset1;//construct without parameter:set space 4

bitset<8> bitset2(12);//the space is 8, storge 12 into binary system,use 0 to fill the blank bit.

string s = "100101";
bitset<10> bitset3(s);//the space is 10,use 0 to fill the blank bit,the string CAN ONLY CONTAINS 0 and 1.

char s2[] = "10101";
bitset<13> bitset4(s2);//the space is 13,use 0 to fill the blank bit

cout << bitset1 << endl;//0000
cout << bitset2 << endl;//00001100
cout << bitset3 << endl;//0000100101
cout << bitset4 << endl;//0000000010101
bitset3[0];//Simular as array,use subscript to access the elements.

There’s so many ways to use bitset, but let’s see struct first.

Struct

A struct is a data structure which contains serval variable type. The struct can also form an array!

C++ examples

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struct Books
{
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
} book = {"C Language", "RUNOOB", "Programing Language", 123456};//define a struct and initialize

//Of course, you can use it as below: No initialize.

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#include <bits/stdc++.h>

using namespace std;

struct student //define the struct of single student
{
    int number;
    int score;
};

int main()
{
	student students[10000];
       for (int i = 0; i < total; i++) //input scores
      {
        cin >> students[i].number >> students[i].score;//See the examples here!
      }

    return 0;

}
//It means you can only define a struct and use it as a data type!
Struct pointer
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#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct student //define the struct of single student
{
    int number;
    int score;
};

int main()
{
    struct student students[100];

    scanf("%d%d", &students[0].number, &students[0].score); //See the examples here!

    struct student *p = students; //initialize the pointer.
    printf("%d", p->number);      
    p++;                          //go to next student.
    return 0;
}
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#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct student
{
    int id;
    int maths;
};

int main()
{
    struct student stu1[2];
    struct student *p ;
    p=stu1;
    
    printf("%d",p->id);

    return 0;
}

Vector

This is a significant data structure in C++ standard library , equals an array that can change memory size at will,and you can also CRUD in it in will.

Basic operations:

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vector<int> c;
c.push_back(1);//place the element at the end of the vector.
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vector<Sales_item> sales_vec;//vector can also store class or struct
vector<vector<string>>;//the elements in this vector are also vector objects.

Other operations:

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vector<T> v1{1,2,3,4,5};
vector<T> v2(5,5);//{5,5,5,5,5}
vector<string> v3={"Hello","World","!"};
vector<int> v4(10); //Create a vector have 10 elements, initialized by 0.
v4.push_back(1);//put an elemnet to the back of the vector;
v4.size();

Use array to initialize a vector 

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int a[]={1,2,3,4,5};
vector<int> v1(begin(a),end(arr));//send the begin and end to construct.

String

String is a char sequence whose size is changeable .

Initialize:

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string s1;//an empty string has been created
string s2(10,'c');//"cccccccccc"

Operations:

Operation Action
os<<s; Write s to ostream
is>>s; Write instream to s
s.size(); Return the length;
s1+s2 Connect two strings
s1>=s2 compare, use dictionary order

Get line

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while(getline(cin,line)&&line.size()>0)
{
    //code
}

Character type:

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tolower(c);//change into lower size
toupper(c);//change into upper size

Warning: Do not do this:

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char a[]="fff";
char b[]="aaa";
string c = a+b;//ERROR: you are trying to add two pointers!!!

Set

An example:

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#include <iostream>
#include <set>

using namespace std;

int main()
{
    int case_number;
    cin >> case_number; //Input the amount
    set<int> numbers;
    int put_number;
    set<int> :: iterator out_number;
    for (int i = 0; i < case_number; i++) // Input data
    {
        cin >> put_number;
        numbers.insert(put_number);
    }
    cout << numbers.size() << endl;
    int count=0;
    for (out_number = numbers.begin(); out_number != numbers.end(); out_number++) 
    {
        
        cout << *out_number ;
        count++;
        if(count <= numbers.size()-1) cout<<" ";
    }

    return 0;
}

Set can automatically sort, and the elements are strictly diverse .

优先队列:优先级最高的元素先出的队列

C++的标准库中包含了一个很好用的数据结构:优先队列.该结构可以将优先级大的元素排到前面.

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#include <bits/stdc++.h>

using namespace std;

int main()
{
	priority_queue<int> que_apples; //默认使用vector,大的数字优先
	priority_queue<int, vector<int>, greater<int>> app_que;//小的数字优先
	
	return 0;
}

自定义优先级:重载运算符

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class Student
{
    int id;
    char name[20];
    bool gender;
    bool operator < (Student &a) const
    {
        return id > a.id;
    }
};

STL算法

快排(sort),包含在algorithm

这个算法极其牛逼,解放了万千程序员的双手(赞美)!!!

快排作用的内容:数组/向量容器等

C++使用实例

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vector<int> v1;
int numbers[2][5];
struct student
{
    int number;
    int score;
    string name;
}
//此处省略若干行插入数据代码,让我们假设这这里面有很多数据
sort(v1.begin(),v1.end());//默认从小到大排列
bool compare(int a , int b)//按某种排序方案排序
{
    return a>b;//这样是降序排列
    return numbers[a][0]>numbers[b][0];//还能读取某些数据的元素排列
    return student[a].score>student[b].score;//还能读取某些结构体的成员
}

常用基础算法(一些很基本的,要背的)

公因数公倍数

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#include <stdio.h>
#include <math.h>
int main()
{
    int m, n;
    int s = 0;
    int min = 0;
    scanf("%d%d", &m, &n);
    //最大公约数
    if (m > n)
    {
        s = m;
        min = n;
    }
    else
    {
        s = n;
        min = m;
    }
    while (min != 0)
    {
        int t = s%min;
        s = min;
        min = t;
    }
    printf("%d\n",s);
    //重置两个数
    if (m > n)
    {
        s = m;
        min = n;
    }
    else
    {
        s = n;
        min = m;
    }
    //公倍数
    for (int i = min;; i += min)
    {
        double resR = (double)i / s;
        int floor = i / s;

        if ((double)floor == resR)
        {
            printf("%d\n", i);
            break;
        }
    }

    return 0;
}

筛法判断质数

上代码:

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bool isPrime(int a)
{
    if (a == 2)
        return true;
    if (a % 2 == 0)
        return false;
    int x = sqrt(a);
    for (int i = 2; i <= x; ++i)
    {
        if (a % i == 0)
            return false;
    }
    return true;
}

素数的埃式筛法

先确认一个数是素数,然后划掉其倍数,在找到下一个素数后,再划掉其倍数,最后只剩素数.

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int main()
{
    int number_list[1000] = {0}; //we can get primes below 1000
    bool break_flag = false;
    number_list[0] = 1;
    int pri = 2;
    while (!break_flag)
    {
        // the non-prime will be mark 1
        int count = pri;
        while (count <= 1000)
        {
            count += pri;
            if (count >= 1000)
                break;
            number_list[count] = 1;
        }
        int temp_pri = pri;
        while (true)
        {
            temp_pri++;
            if (temp_pri >= 999)
            {
                break_flag = true;
                break;
            }
            if (number_list[temp_pri] == 0)
            {
                pri = temp_pri;
                break;
            }
        }
    }
    for (int i = 0; i < 1000; i++)
    {
        if (number_list[i] == 0)
        {
            cout << i << " ";
        }
    }

    return 0;
}

分解质因数(简便方法)

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#include <stdio.h>
#include <math.h>
//这个程序适合好好阅读并分析
void foo(long long int n)
{
    long long int sqr = sqrt(n);//测试质数只需测到平方的取整
    long long int i = 0;
    for(i = 2; i <= sqr; i++)//从2开始测
    {
        if(n % i == 0 && (n /= i))//后面的表达式指的是除i留下剩余部分
        {
            printf("%lld ", i--);
        }
    }
    if(n != 1)//不打印1作为因子
    {
        printf("%lld", n);
    }
    printf("\n");
}

int main()
{
    long long int n ;
    scanf("%lld", &n);
    foo(n);
    return 0;
}

查找字符(这是C标准库里的内容)

用于在一个字符串(也就是char数组)中查找指定的字符

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strchr(string_name, 'A');//在string name 这个字符串中寻找A这个字符
//返回有多种可能,若找到,返回指向这个字符的指针,否则返回NULL(这个NULL是标识符,不是字符串之类的玩意)

位运算

位运算是一种直接操作位的运算,其包含多种运算符:

上代码:

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<<; //左移运算符,移动时丢弃左边的位,用0补充
"11110000"<<"10000000";//左移了3位!!!
>>; //右移运算符,移动时丢弃右边的位,左边用0或原来丢弃的左边的位补充!!!
"11111111">>"00001111";//右移了四位!!!
    
//接下来看看逻辑位运算
~;//按位非,倒置0/1
|;//按位或,有一为1,否则为0
^;//XOR,相同为0,不同为1
&;//AND,都为1才为1,否则为0

//一些常用的位逻辑运算:
lottabits |= pow(2,3);//打开位,也就是将某一位置为1,其中后面的2的多少次方代表着打开的位置(2的0次方代表右起第一位,以此类推)
lottabits ^= pow(2,3);//切换位:置反
lottabits &= pow(2,3);//关闭位:置0
bool isOpen = lottabits & pow(2,3);//测试某一位是否为1(打开),返回true or false.