All 32 keyword classifications of C language C89 (C90)

Data type key (12 individual )

char ： Declare character type variables or functions

short ： Declare short integer variables or functions

int ： Declare an integer variable or function

long ： Declare long integer variables or functions

signed ： Declare a symbolic type variable or function

unsigned ： Declare an unsigned type variable or function

float ： Declare floating-point variables or functions

double ： Declare a double precision variable or function

struct ： Declare a structural variable or function

enum ： Declare enumeration type

void ： Declares that the function returns no value or takes no arguments , Declare no type pointer

Control statement keywords (12 individual )

1. Cycle control （5 individual ）

• for ： A circular statement
• do ： The body of a loop statement
• while ： The loop condition of a loop statement
• break ： Jump out of current loop
• continue ： End the current cycle , Start next cycle

2. Conditional statements （3 individual ）

• if : Conditional statements
• else ： Conditional statement negates Branch
• goto ： Jump statements without conditions

4. Switch statement （3 individual ）

• switch : For switch statements
• case ： Switch statement Branch
• default ： In the switch statement “ other ” Branch

5. Return statement （1 individual ）

• return ： Function return statement ( With parameters , Also see without parameters )

Storage type key （5 individual ）

• auto ： Declare automatic variables , Generally not used
• extern ： Declared variables are declared in other files
• register ： Declare register variables
• static ： Declare static variables
• typedef ： Used to alias data types ( However, the keyword is classified into storage keyword categories , Although it doesn't seem relevant )

Other keywords （3 individual ）

• const ： Declare read-only variable
• sizeof ： Calculate the data type length
• volatile ： Explain that variables can be implicitly changed during program execution