c++从入门到精通——基本入门

C++

-1.helloWorld

#include <iostream>

using namespace std;
int main(){

    cout<<"hello world!"<<endl;
    system("pause");
    return EXIT_SUCCESS;
}

• 双冒号作用域

#include <iostream>
using namespace std;
void test01(){
    int atk = 1000;
    std::cout<<"atk="<<atk<<std::endl;
    std::cout<<"atk="<<atk<<std::endl;
}
int main(){
    test01();
    system("pause");
    return EXIT_SUCCESS;
}

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>

using namespace std;

int getRectS(int w,int h);

int getRectS(int w, int h) {
    return w*h;
};
void test01(){
    printf("%d\n",getRectS(10,10));
}
void* test02(){
    char *p = (char *) malloc(sizeof(char ));
    *p = '2';
    printf("p的地址:%p",&p);
    printf("%d",*p);
    printf("p的地址:%p",p);
    printf("\n");
    return p;
}

int main(){
    test01();
    char *p = (char*)test02();
    printf("%d",*p);
    printf("p的地址:%p",&p);


    return 0;
}

• 引用

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;

//���û����﷨��  ����  &���� = ԭ��
void test01()
{
  int a = 10;
  int &b = a;

  b = 100;
  cout << "a = " << a << endl;
  cout << "b = " << b << endl;
}


void test02()
{
  int a = 10;
  //int &b; 
  int &b = a;


  int c = 100;

  b = c; 

  cout << "a = " << a << endl;
  cout << "b = " << b << endl;
  cout << "c = " << c << endl;
}

//�����齨������
void test03()
{
  //1��ֱ�ӽ�������
  int arr[10];
  int(&pArr)[10] = arr;

  for (int i = 0; i < 10; i++)
  {
    arr[i] = 100 + i;
  }
  for (int i = 0; i < 10; i++)
  {
    cout << pArr[i] << endl;
  }


  //2���ȶ�����������ͣ���ͨ������ ��������
  typedef int(ARRAY_TYPE)[10];
  //����  &���� = ԭ��
  ARRAY_TYPE & pArr2 = arr;

  for (int i = 0; i < 10; i++)
  {
    cout << pArr2[i] << endl;
  }

}

int main(){

  //test01();
  //test02();
  test03();

  system("pause");
  return EXIT_SUCCESS;
}

• 命名空间

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;

namespace KingGlory
{
    int sunwukongId = 1;
}

namespace LOL
{
    int sunwukongId = 3;
}

void test01()
{
    int sunwukongId = 2;

    //1、using声明
    //using KingGlory::sunwukongId ;

    //当using声明与 就近原则同时出现，出错，尽量避免
    cout << sunwukongId << endl;

}


void test02()
{
    //int sunwukongId = 2;
    //2、using编译指令
    using namespace KingGlory;
    using namespace LOL;
    //当using编译指令  与  就近原则同时出现，优先使用就近
    //当using编译指令有多个，需要加作用域 区分
    cout << KingGlory::sunwukongId << endl;
    cout << LOL::sunwukongId << endl;
}

int main(){

    //test01();
    test02();
    system("pause");
    return EXIT_SUCCESS;
}

对C语言的增强

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;

//1、全局变量检测增强  C++检测出重定义
int a;
//int a = 10;

//2、函数检测增强 返回值检测、形参类型检测、函数调用参数个数
int getRectS(int w,int h)
{

    return w *h;
}
void test01()
{
    printf("%d\n", getRectS(10, 10));
}


//3、类型转换检测增强
void test02()
{
    char * p = (char *)malloc(64);
}

//4、struct增强  C++可以放函数，创建结构体变量，可以简化关键字 struct
struct Person
{
    int age;
    void func()
    {
        age++;
    }
};

void test03()
{
    Person p;
    p.age = 17;
    p.func();
    cout << "p的age = " << p.age << endl;
}

//5、bool类型扩展  C语言下 没有这个类型  C++有bool类型
bool flag = true; // bool类型 代表  真和假   true  ---- 真(1)    false  ---- 假(0)

void test04()
{
    cout << sizeof(bool) << endl; //结果是1个字节
    //flag = false;
    //flag = 100; //将非0的数都转为1
    cout << flag << endl;
}

//6、三目运算符增强
void test05()
{
    //?:
    int a = 10;
    int b = 20;

    printf("ret = %d\n", a > b ? a : b);

    (a < b ? a : b )= 100; // C++下返回的是变量  b = 100

    printf("a = %d\n", a);
    printf("b = %d\n", b);
}


//7、const增强
//全局const   和C语言结论一致
const int m_A = 100;
void test06()
{
    //m_A = 200;
    //int * p = (int *)&m_A;

    //*p = 200;


    //局部const
    const int m_B = 100;
    //m_B = 200;
    int * p = (int *)&m_B;
    *p = 200;
    cout << "m_B = " << m_B << endl;

    int arr[m_B]; //C++下const修饰的变量 称为常量 ，可以初始化数组

}


int main(){
    test01();
    test03();
    test04();
    test05();
    test06();


    system("pause");
    return EXIT_SUCCESS;
}

引用其他变量

test.cpp

extern const int g_a = 1000;

main.cpp

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.h>

int main(){
    extern const int g_a;
    printf("g_a = %d\n", g_a);
    system("pause");
    return EXIT_SUCCESS;
}

引用的基本使用

#include <iostream>
using namespace std;

void test01(){
    int a=10;
    int &b = a;
    b = 100;
    cout << "a = " << a << endl;
    cout << "b = " << b << endl;
}
void test02()
{
    int a = 10;
    //int &b; //引用必须要初始化

    int &b = a;

    //引用一旦初始化后，就不可以引向其他变量

    int c = 100;

    b = c; // 赋值
    printf("%p\n",&b);
    printf("%p\n",&a);
    printf("%p\n",&c);
    cout << "a = " << a << endl;
    cout << "b = " << b << endl;
    cout << "c = " << c << endl;
}
//对数组建立引用
void test03()
{
    //1、直接建立引用
    int arr[10];
    int(&pArr)[10] = arr;

    for (int i = 0; i < 10; i++)
    {
        arr[i] = 100 + i;
    }
    for (int i = 0; i < 10; i++)
    {
        cout << pArr[i] << endl;
    }
    //2、先定义出数组类型，再通过类型 定义引用
    typedef int(ARRAY_TYPE)[10];
    //类型  &别名 = 原名
    ARRAY_TYPE & pArr2 = arr;
    for (int i = 0; i < 10; i++)
    {
        cout << pArr2[i] << endl;
    }

}
int main(){

    test01();
    test02();
    return 0;
}

引用注意事项

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;

//1、值传递
void mySwap01(int a  , int b)
{
    int temp = a;
    a = b;
    b = temp;

    /*cout << ":::a = " << a << endl;
    cout << ":::b = " << b << endl;*/
}

//2、地址传递
void mySwap02(int *a, int *b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}

//3、引用传递
void mySwap03(int &a , int &b) // int &a = a; int &b = b;
{
    int temp = a;
    a = b;
    b = temp;
}

void test01()
{
    int a = 10;
    int b = 20;
    //mySwap01(a, b);
    //mySwap02(&a, &b);

    mySwap03(a, b);

    cout << "a = " << a << endl;
    cout << "b = " << b << endl;
}

int& func()
{
    int a = 10;
    return a;
}

//引用注意事项
void test02()
{
    //1、引用必须引一块合法内存空间
    //int &a = 10;

    //2、不要返回局部变量的引用
    int &ref = func();
    cout << "ref = " << ref << endl;
    cout << "ref = " << ref << endl;
}

int& func2()
{
    static int a = 10;
    return a;
}

void test03()
{
    int &ref = func2();
    cout << "ref = " << ref << endl;
    cout << "ref = " << ref << endl;
    cout << "ref = " << ref << endl;
    cout << "ref = " << ref << endl;
    //当函数返回值是引用，那么函数的调用可以作为左值
    func2() = 1000;
    cout << "ref = " << ref << endl;


}


int main(){
    //test01();
    //test02();
    test03();
    system("pause");
    return EXIT_SUCCESS;
}

指针引用

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>

using namespace std;
struct Person {
    int age;
};

void allocateSpace(Person **p) {
    //p指向指针的指针    *p  指针 指向的是person 本体   **p  person本体
    printf("%p\n",p);
    printf("%p\n",*p);
//    printf("%p\n",*p);
    *p = (Person *) malloc(sizeof(Person));
    (*p)->age = 10;
}

void test01() {
    Person *p = NULL;
    allocateSpace(&p);
    cout<<"p.age = "<<p->age<<endl;
};

void allocateSpace2(Person* &pp){
    pp = (Person*) malloc(sizeof (Person));
    pp->age = 20;
};

void test02(){
    Person *p = NULL;
    allocateSpace2(p);
    cout<<"p.age="<<p->age<<endl;
};
int main(){
    test01();
    test02();
    return EXIT_SUCCESS;

}

常量引用

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>

using namespace std;

void test01() {
  const int &ref = 10; // 加了const之后，  相当于写成   int temp = 10;  const int &ref = temp;
  printf("%p\n",&ref);
  int *p = (int *)&ref;
  printf("%p\n",p);
  *p = 10000;
  cout<<"ref="<<ref<<endl;
};
void showValue(const int &a){
  //常量引用的使用场景 修饰函数中的形参，防止误操作
//  a = 100000000;
  cout<<"a"<<a<<endl;

};
void test02(){

  int a=100;
  showValue(a);
}



int main() {
  test01();
  test02();
  return EXIT_SUCCESS;

}