Self taught structure (small turtle C language)

The following is in b The little turtle watching from the station c Language when recorded with video code

What kind of structure is it , How to use a structure ？

Take the following code as an example

# include <stdio.h>

struct Book   // Define the key of a structure struct  And the name of the structure is Book Note that the initial is usually capitalized 
{
    
	char title[128];    // Our function is to store the name of the book , author , And the price , Plate number 
	char author[48];    // Inside the braces are structural members 
	float price;
	unsigned int date;
	char pulisher[48];

}book;    // This is the name of the structure variable , Be similar to  int book  Medium book Is the variable name of the integer , there book Is the structure type , The structure is called Book The variable of book. There is a little detour here .

void main(void)// The main function 
{
    
		While(1);// Do nothing for the time being 

}

Another way to define a structure is

# include <stdio.h>

struct Book   // Define the key of a structure struct  And the name of the structure is Book Note that the initial is usually capitalized 
{
    
	char title[128];    // Our function is to store the name of the book , author , And the price , Plate number 
	char author[48];
	float price;
	unsigned int date;
	char pulisher[48];

};    // Note that only the name of the structure is defined here , Instead of creating variables .

void main(void)// The main function 
{
    
		Struct Book book;// Here is the creation of a Book Variable of structure type book

}

The next step is how to access structure variables ？
The member of the access structure introduces a new symbol “ Order number ”——“.”
such as book.title It's quoting Book Structure of the title member , obviously title The member is an array of characters .
and book.price Is quoted Book Structure of the price member , and price Is a floating-point variable .

Next, continue to look at the program

# include <stdio.h>


struct Book
{
    
	char title[128];
	char author[48];
	float price;
	unsigned int date;
	char pulisher[48];

}book;



void main(void)
{
    
	printf(" Please enter the title of the book  \n");
	scanf("%s",book.title);   // This involves assignment 

	printf(" Please enter the author  \n");
	scanf("%s",book.author);

	printf(" Please enter the selling price  \n");
	scanf("%f",&book.price);

	printf(" Please enter the date of publication  \n");
	scanf("%d",&book.date);

	printf(" Please enter the publishing house  \n");
	scanf("%s",book.pulisher);

	printf("************ Data entry completed ************\n");

	printf(" Title ：%s\n",book.title);
	printf(" author ：%s\n",book.author);
	printf(" The price is ：%f\n",book.price);
	printf(" Publication date ：%d\n",book.date);
	printf(" Press. ：%s\n",book.pulisher);

}

Initializing structure variables
Initialize a variable and an array

Int a = 520;
Int array[5]={
    1,2,3,4,5};

 Initialize a structure variable 
Struct Book book ={
    
“ Little turtle takes you flying ”,  // Be careful to separate them with commas , Also note that it must correspond to the defined structure member types 
“ Little turtle ”,
9.9,
20170707,
“ tsinghua ”
};

Initializes the specified member value of the structure
Its syntax is similar to that of an array specifying initialization elements , However, the struct specifies that initialization members use “ Order number ”——“.” Operator and member name
For example, initialization book Of price member ：

Struct Book book = {
    .price = 9.9};
 You can also initialize without the order of members declared by the structure ：
Struct Book book = {
    
.publisher = “ tsinghua ”,
.price = 9.9,
.date = 20170707
};

The system will align the memory

# include <stdio.h>

void main (void)

{
    
	struct A
	{
    
		char a;
		int b;
		char c;

	
	}a = {
    'x',250,'c'};

	printf("size of a = %d \n",sizeof(a));


}

Theoretically, the above procedure is x Station one byte ,250 Occupy 4 Bytes ,c Take up a byte
The actual output is 12 Bytes
Each of them is in accordance with 4 Byte processing is old 12 Bytes
If you change the order of output x,o,250
The output of 8 Bytes
because , The first two character types each occupy 2 Bytes , But the system will automatically supplement 2 Bytes , Take up a total of 4 Bytes , and 250 It is assigned by itself 4 Bytes .

Structure array and structure pointer
Nested structure

# include <stdio.h>

struct Date
{
    
	int year;
	int month;
	int day;
};

struct Book
{
    
	char title[128];
	char author[48];
	float price;
	struct Date date;// junction á structure 1 body ? Of ? Embedded ? set ?
	char pulisher[48];

}book = {
    
	" Little turtle ,
	" Little turtle ",
	9.9,
	{
    2017,1,11},
	" Tsinghua University "
};

void main(void)
{
    

	printf(" Title ：\n",book.title);
	printf(" author ：%s\n",book.author);
	printf(" The price is ：%f\n",book.price);
	printf(" Publication date ：%d-%d-%d\n",book.date.year,book.date.month,book.date.day);   // Be sure to access the bottom layer 
	printf(" Press. ：%s\n",book.pulisher);

}

Array of structs
The first one is ： Define when declaring a structure
Struct Structure name
{
Structural members ;

} Array name [ length ];

The second kind ： A structural type is indicated first （ Like the one above Book）, Then define a structure array with this type .
Struct Structure name
{
Structural members ;

};
Struct Structure name Array name [ length ];

Initializing the array of structs
Struct Book book[3] = {
{“< Zero basis >”,” Little turtle ”,9.9,{2017,11,7},” tsinghua ”},
{“ introduction ”,” Soft shelled turtle ”,9.9,{2017,10,1},” tsinghua ”},
{“ To the earth ”,“ fish ”,9.9,{2017,9,9},” tsinghua ”},
};

Structure pointer
Struct Book * pt; // Make a statement Book Pointer variable of type structure pt
Here's a little bit of attention , The variable name of the array represents the first address of the array , So the array name can be directly assigned to the pointer variable . The variable name of the structure pointer needs to use “&” The address can be given to the structure variable .
We need to add one more pt = &book;

There are two ways to access structure members through structure pointers ：
The first one is ：
（ Structure pointer ）. Member name
Be careful ： The parentheses are added here because “.” Operators take precedence over “” Operator .
The second kind ：
Structure pointer -> Member name
Be careful “->” There must be no space between them , In addition, his priorities are similar to “.” The priority of is the same .
The above two are completely equivalent

The first way to quote is as follows ：

# include <stdio.h>

struct Date
{
    
	int year;
	int month;
	int day;
};

struct Book
{
    
	char title[128];
	char author[48];
	float price;
	struct Date date;// junction á structure 1 body ? Of ? Embedded ? set ?
	char pulisher[48];

}book = {
    
	" Little turtle flies ,
	" Little turtle ",
	9.9,
	{
    2017,1,11},
	" Tsinghua University "
};



void main(void)
{
    
	struct Book*pt;
	pt = &book; 


	printf(" Title ：%s\n",(*pt).title);
	printf(" author ：%s\n",(*pt).author);
	printf(" The price is ：%0.2f\n",(*pt).price);
	printf(" Publication date ：%d-%d-%d\n",(*pt).date.year,(*pt).date.month,(*pt).date.day);   
	printf(" Press. ：%s\n",(*pt).pulisher);

}

The second way to quote

# include <stdio.h>

struct Date
{
    
	int year;
	int month;
	int day;
};

struct Book
{
    
	char title[128];
	char author[48];
	float price;
	struct Date date;// Nesting of structures 
	char pulisher[48];

}book = {
    
	" Little turtle flies ,
	" Little turtle ",
	9.9,
	{
    2017,1,11},
	" Tsinghua University "
};



void main(void)
{
    
	struct Book*pt;
	pt = &book; 


	printf(" Title ：%s\n",pt->title);
	printf(" author ：%s\n",pt->author);
	printf(" The price is ：%0.2f\n",pt->price);
	printf(" Publication date ：%d-%d-%d\n",pt->date.year,pt->date.month,pt->date.day);   	 	printf(" Press. ：%s\n",pt->pulisher);

}