Day 3 array, pre post, character space, keyword and address pointer

1. You cannot use variables to specify the size of an array

example ：

int a=10;

int  arr[a]={0};

This program is wrong .

It can be seen from the above , Spaces and default added “\d” Also count one character respectively . But notice that "\0" The length of the string is not counted . But a space is a character .

2. Find the space occupied by characters

3. Front and back

4. key word

struct     Structure keywords

union     Consortium / Shared body

typedef  The type definition

static  int  a        Static local variables a, When modifying a local variable , Will make the life cycle of local variables longer

Don't use static when ：

Use static when ：

static  When modifying global variables , Will change the scope of the global variable , Make global variables available only in the source file where they are located .

for example ：

In the source file test_1 in ：

int  change_1=25;

In the source file test_2 in :

extern int chang_1

here chang_1 Can be in test_2 Use in , But if it is

static int  change_1=25;

here chang_1 Not in test_2 Use in

5.#define Define constants and macros

6. Address of a pointer