c++基础语法

当当当当！

时间过的真的好快，C语言已经学完了，开始学c++了，博客也没有坚持写，新阶段新开始嘛，希望能按时写奥！

• 命名空间

       作用域：不可以在同一个作用域下声明两个相同名字的变量

#include <iostream>
using namespace std;
int age = 300;//注释掉这行
namespace Person
{
    int age = 200;
}
namespace Bird
{
    int age = 100;
    int sex = 101;
}
using namespace Bird;
int main()
{
    cout<<::age<<endl;//查看这行变化   全局变量优先级高
    cout<<Person::age<<endl;
    cout<<Bird::age<<endl;
    cout<<::sex<<endl;
}

• new delete

#include <iostream>
using namespace std;
int main()
{
    int *p = new int;
    *p = 10;
    cout<<*p<<endl;
    delete p;
    p = 0;

    int *arr = new int[10];
    arr[0] = 0;
    arr[1] = 1;
    cout<<arr[0]<<" "<<arr[1]<<endl;
    cout<<arr<<endl;
    delete[] arr;//delete 数组要加[]
    //cout<<arr<<endl;
    //delete之后指针还指向地址，但该空间已经不属于我，不要对它进行操作！
    arr = 0;

    int *a = new int(10);//将a指向的int初始化为10
    cout<<*a<<endl;
    delete a;
    a = 0;
}

• 缺省函数参数

#include <iostream>
using namespace std;

void Show(int a ,int b , int c = 2, int d = 3);
int main()
{
    Show(100,200);
    int arr[10] = {0,1,2,3,4,5,6,7,8,9};
}
//不能再函数实现中加参数，如果函数声明中已存在则重复定义，如果没有则格式错误
void Show(int a  ,int b , int c  , int d )
{
    cout << a << " " << b <<endl;
    cout << c << " " << d <<endl;
}

• for循环

for(auto i : arr)//auto可自动识别arr中类型
{
    cout<< i << " ";
}

•  函数重载

函数名相同，函数参数个数或类型不同

• 引用

值传递，地址传递和引用

#include <iostream>
using namespace std;
void Num(int a,int b);
void Adress(int *a,int *b);
void Yinyong(int &aa, int &bb);
int main()
{
    int a = 5;
    int b = 6;
    cout<<a<<" "<< b<<endl;
    Num(a,b);
    cout<<a<<" "<< b<<endl;
    Adress(&a,&b);
    cout<<a<<" "<< b<<endl;
    Yinyong(a,b);
    cout<<a<<" "<< b<<endl;

}
void Num(int a,int b)
{
    int c;
    c = a;
    a = b;
    b = c;
}
void Adress(int *a,int *b)
{
    int c = *a;
    *a = *b;
    *b = c;
}
void Yinyong(int &a, int &b)
{
    int c;
    c = a;
    a = b;
    b = c;
}