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C basic grammar
2022-07-06 16:04:00 【Programming fish 66】
We have seen C The basic structure of the program , This will help us to understand C Other basic building blocks of language .
C The token (Token)
C The program consists of various tokens , Tokens can be keywords 、 identifier 、 Constant 、 A string value , Or a symbol . for example , Below C The statement includes five tokens :
printf("Hello, World! \n");
The five tokens are :
printf
(
"Hello, World! \n"
)
;
A semicolon ;
stay C In the program , Semicolons are statement terminators . in other words , Each statement must end with a semicolon . It shows the end of a logical entity .
for example , Here are two different statements :
printf("Hello, World! \n");
return 0;
notes
C There are two ways to annotate a language :
// Single-line comments
With // The first single line comment , This comment can take up a single line .
/* Single-line comments */
/*
Multiline comment
Multiline comment
Multiline comment
*/
/* */ Comments in this format can be one or more lines .
You cannot embed comments in comments , Comments cannot also appear in strings or character values .
identifier
C Identifiers are used to identify variables 、 function , Or any other user-defined project name . An identifier is in letters A-Z or a-z Or the underscore _ Start , Followed by zero or more letters 、 Underline and numbers (0-9).
C Punctuation characters... Are not allowed in identifiers , such as @、$ and %.C yes Case sensitive Programming language . therefore , stay C in ,Manpower and manpower Are two different identifiers . A few valid identifiers are listed below :
mohd zara abc move_name a_123 myname50 _temp j a23b9 retVal
keyword
The following table lists them C Reserved word in . These reserved words cannot be used as constant names 、 Variable name or other identifier name .
keyword | explain |
---|---|
auto | Declare automatic variables |
break | Jump out of current loop |
case | Switch statement Branch |
char | Declare a character variable or function return value type |
const | Define constants , If a variable is const modification , Then its value can no longer be changed |
continue | End the current cycle , Start next cycle |
default | In the switch statement " Other " Branch |
do | The body of a loop statement |
double | Declare a double precision floating-point variable or function return value type |
else | Conditional statement negates Branch ( And if Continuous use ) |
enum | Declare enumeration type |
extern | Declare that variables or functions are defined in other files or other locations in this file |
float | Declare floating point variable or function return value type |
for | A circular statement |
goto | Jump statements without conditions |
if | Conditional statements |
int | Declare an integer variable or function |
long | Declare long integer variable or function return value type |
register | Declare register variables |
return | Subroutine return statement ( With parameters , Or without parameters ) |
short | Declare short integer variables or functions |
signed | Declare a symbolic type variable or function |
sizeof | Calculate data type or variable length ( That is, the number of bytes ) |
static | Declare static variables |
struct | Declare the struct type |
switch | For switch statements |
typedef | Used to alias data types |
unsigned | Declare an unsigned type variable or function |
union | Declare the common body type |
void | Declares that the function returns no value or takes no arguments , Declare no type pointer |
volatile | Explain that variables can be implicitly changed during program execution |
while | The loop condition of a loop statement |
C99 New keyword
_Bool | _Complex | _Imaginary | inline | restrict |
C11 New keyword
_Alignas | _Alignof | _Atomic | _Generic | _Noreturn |
_Static_assert | _Thread_local |
C Spaces in
Lines that contain only spaces , It's called a blank line , Maybe with comments ,C The compiler will completely ignore it .
stay C in , Spaces are used to describe spaces 、 tabs 、 Line breaks and comments . Spaces separate parts of a statement , Let the compiler recognize an element in a statement ( such as int) Where to end , Where does the next element start . therefore , In the following sentence :
int age;
ad locum ,int and age There must be at least one space character between ( It's usually a blank character ), So that the compiler can distinguish them . On the other hand , In the following sentence :
fruit = apples + oranges; // The total number of fruits obtained
fruit and =, perhaps = and apples The space character between is not required , But to enhance readability , You can add some spaces as needed .
resources & More in-depth readings :
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