C secret arts script Chapter 5 (structure) (Section 1)

I haven't seen you for many days , Dear Taoist friends , Here comes our new chapter , The data types we saw in the previous chapters are c Language built-in data types , Such as int,float,char.... We know ,c Language has custom functions , Users can design a function according to the functions they need , Does our data type have a user-defined type ？ The answer is yes ： The first one we want to introduce in this chapter Custom data types —— Structure .

 1. What is a structure ： A structure is a collection of values , These values are called member variables , Each member of the structure can be a variable of different data types .

2, Declaration and definition of structure

#include<stdio.h>
struct stu
{
    char name[6];
    int age;
    double score;    // Declaration of a structure 
};
int main()
{
    struct stu s1={
    {" Zhang San "},{17},{456.0}};        // Definition of structure 
    return 0;
}

Be careful ：

1. It's defined in main Structural variables within functions or other functions are local variables , If created in struct{} Variable name ;         Here is the global variable .

The following code ：

#include<stdio.h>
struct stu
{
    char name[6];
    int age;
    double score;    // Declaration of a structure 
}stu;        // Global variable definition of structure 

2. Anonymous declaration of structure ：

Such as ：

#include<stdio.h>
struct
{
    int a;
    char b;
    float c;
};

    This structure has no definition. The structure data type name cannot be in main Function or other functions , Only in struct{} Variable name ; Here to create .

Such as ：

#include<stdio.h>
struct
{
    int a;
    char b;
    float c;
}S;

3. Self reference of structure

        It sounds like functional recursion , Call yourself .

Such as ：

#include<stdio.h>
struct node
{
    int cor;
    struct node n;
};
int main()
{
    sizeof(struct node);
    return 0;
}

        It looks like there's nothing wrong with it , But this code is wrong ,struct node n Call yourself , Each structure has a int cor, Then call yourself ,sizeof How big is the calculated space , This is immeasurable, so this structure self reference is wrong .

Correct self reference method ：

#include<stdio.h>
struct node
{
    int cor;
    struct node* n;
};
int main()
{
    sizeof(struct node);
    return 0;
}

We write self reference members as structure pointers , Only pointers can find structures of the same type , And the size of the pointer is fixed 4/8.

4.typedef Keyword decorated structure

typedef Keyword can rename the data type , Structure types are no exception .

Such as ：

#include<stdio.h>
typedef struct node
{
    int a;
    char b;
}node;        

Be careful ：typedef A modified structure {}; The variables between are not global variables , It was renamed node Of struct node Structure type name .

2.typedef Decorate anonymous structures

#include<stdio.h>
typedef struct 
{
    int a;
    char b;
}node;        

This writing is wrong , The structure type has not been named yet , How to rename ？ Isn't it a question of chicken or egg first ？

        Okay , That's all for this section , Dear Taoist friends , The coming days would be long , I'll see you in the next section ！