c++基础语法

 1 #include <iostream>
 2 using namespace std;
 3 int age = 300;//注释掉这行
 4 namespace Person
 5 {
 6     int age = 200;
 7 }
 8 namespace Bird
 9 {
10     int age = 100;
11     int sex = 101;
12 }
13 using namespace Bird;
14 int main()
15 {
16     cout<<::age<<endl;//查看这行变化   全局变量优先级高
17     cout<<Person::age<<endl;
18     cout<<Bird::age<<endl;
19     cout<<::sex<<endl;
20 }

 1 #include <iostream>
 2 using namespace std;
 3 int main()
 4 {
 5     int *p = new int;
 6     *p = 10;
 7     cout<<*p<<endl;
 8     delete p;
 9     p = 0;
10 
11     int *arr = new int[10];
12     arr[0] = 0;
13     arr[1] = 1;
14     cout<<arr[0]<<" "<<arr[1]<<endl;
15     cout<<arr<<endl;
16     delete[] arr;//delete 数组要加[]
17     //cout<<arr<<endl;
18     //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！
19     arr = 0;
20 
21     int *a = new int(10);//将a指向的int初始化为10
22     cout<<*a<<endl;
23     delete a;
24     a = 0;
25 }

 1 #include <iostream>
 2 using namespace std;
 3 
 4 void Show(int a ,int b , int c = 2, int d = 3);
 5 int main()
 6 {
 7     Show(100,200);
 8     int arr[10] = {0,1,2,3,4,5,6,7,8,9};
 9 }
10 //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
11 void Show(int a  ,int b , int c  , int d )
12 {
13     cout << a << " " << b <<endl;
14     cout << c << " " << d <<endl;
15 }

1 for(auto i : arr)//auto可自动识别arr中类型
2 {
3     cout<< i << " ";
4 }