List item

Constant

***> C There are several constants in the language

Literal constants ： Integer constant 、 Floating-Point Literals 、 character constants , Or string literals such as ：123,‘w’,Abc etc.
const Modified constant variable
#define The defined identifier constant
Enumeration constants ***

const Modify the constant

const Before finishing ,a The value of can be changed .

const After retouching ,a The value of can no longer change

So const The modifier is a constant variable , That is, the variable is essentially a variable , however const Gives it a constant property

#define The defined identifier constant

We usually #define The following constant name is set to uppercase （ It's a habit ）, Of course, it can also be set to lowercase letters, etc
#define Not only can you define numeric constants , You can also define characters , String and other constants .

Enumeration constants

Enumeration constant format

enum A                  //  Equivalent to a type 
{
    
  BOY,
  GIRL
};                     //  Note that you don't have to... In braces ; Comma , After the curly braces, use ;

int main()
{
    
	enum A c = GIRL;   // enum A  Equivalent to a variable type , here c The value range of can only be in braces BOY or GIRL
	return 0;

}

character string + Escape character + notes

character string

stay C In language, double quotation marks "" What is referenced is called a string , Such as ：“abcdef”, A... Is hidden at the end of the string \0 As the end of the string , But this is not counted as the content of the string

\0 The role of

We can see arr There are double quotes in the array , That is to say \0, and arr1 There are no double quotes in the array ,arr The printed value of the array is normal ,arr1 The array prints out ab It's worth more after , This is because \0 Is the end of string flag , When printf encounter \0 after , End to perform , and arr1 No, \0, So when he finished printing ab after , It will continue to hit , Know to meet \0 until

Escape character

Some letters are defined in and preceded by "" To show the common things that can't be shown ASCII character , Such as \0,\t,\n etc. , It's called an escape character , Because of the following characters , It's not the original ASCII The character means
Columns such as ： We print on the computer \test

We will find that t Be missing ,est There are many spaces in front
This is because in the C When in language \ Followed by t formation \t when , It will become another meaning , We put this \ Characters that, together with other characters, will become another expression are called escape characters

Escape character	meaning
?	Use... When writing multiple consecutive question marks , Prevent them from being parsed into three letter words
’	Used to represent character constants ’
\“	Double quotation marks used to represent the inside of a string
\	Used to indicate a backslash , Prevent it from being interpreted as an escape sequence character .
\a	Warning characters , Beep
\b	Back space
\f	Paper in
\n	Line break
\r	enter
\t	Horizontal tabs
\v	Vertical tabs
\ddd	ddd Express 1~3 Eight octal numbers . Such as ： \130 X
\xdd	dd Express 2 Hexadecimal numbers . Such as ： \x30 0
Particular attention ：8 Cannot appear in hexadecimal 8,16 Cannot appear in hexadecimal 16
\628 Originally meet \ddd Escape character ,ddd It means 1-3 Brother 8 Decimal digit , But here comes 8, therefore \62 Is a character ,8 Single character , No longer \628 As a character

The use of annotations

notes ： Screen out some unnecessary code , Or explain some special code

We can use \ Comment on a line of code or add corresponding explanation after this line of code .

** We can also use "/“ As the beginning ”/" As a conclusion, comment on many lines of code **
stay VS In the compiler, we can use the key indicated by the red arrow to comment , The key indicated by the blue arrow cancels the comment .

Select statement

Here we use if else Statement to illustrate

Loop statement

C In language while sentence for sentence
do…while sentence
Here we use while Statement to illustrate

function

Just like the function in our mathematics , When you enter a value into it , It will be executed according to the rules of the function , And get the corresponding result

This is a simple addition function , After entering any two values , This function will follow the rules of its internal addition , Operate on these two numbers , And get the corresponding result .

Array

When we want to store a long string of characters ,C The language specifies that arrays should be used to store .

int arr[10]={
    1,2,3,4,5,6,7,8,9,10};// Define an integer array , Inside 10 Brother element 

stay C In language , The array has the following table

Array name arr hinder [] The size of the array can be set in ,[] The number inside must be a constant ,

[] The value in cannot be a constant variable , Because the essence of a constant variable is a variable

Must be constant

Use of arrays

#include <stdio.h>
int main()
{
    
 int i = 0;
 int arr[10] = {
    1,2,3,4,5,6,7,8,9,10};
 for(i=0; i<10; i++)
 {
    
       printf("%d ", arr[i]);
 }
 printf("\n");
    return 0;
}