C Keywords Reference
C Keywords Reference
In C Keywords Reference are reserve words that have special meaning in the C language. You cannot use them as variable names, function names, or identifiers. They form the core syntax of C.
List of C Keywords (C99 Standard)
| Keyword | Description |
|---|---|
auto | Default storage class for local variables |
break | Exit from loops or switch |
case | Defines a branch in a switch statement |
char | Character data type |
const | Defines a constant value |
continue | Skip to next iteration of a loop |
default | Default branch in switch statement |
do | Do-while loop |
double | Double-precision floating-point data type |
else | Alternative branch in if-else |
enum | Defines an enumeration (set of named constants) |
extern | Declares a variable/function defined elsewhere |
float | Floating-point data type |
for | For loop |
goto | Jump to a labeled statement |
if | Conditional statement |
inline | Suggests compiler to inline a function |
int | Integer data type |
long | Long integer data type |
register | Suggests storing variable in CPU register |
restrict | Pointer optimization hint (C99) |
return | Exit from a function and return a value |
short | Short integer data type |
signed | Signed integer |
sizeof | Returns size of a type or variable in bytes |
static | Preserves variable value between function calls; file-level scope |
struct | Defines a structure |
switch | Switch-case control statement |
typedef | Defines a new type name |
union | Defines a union |
unsigned | Unsigned integer |
void | Function returns nothing or empty pointer type |
volatile | Tells compiler variable can change unexpectedly |
while | While loop |
_Bool | Boolean type (C99) |
_Complex | Complex number type (C99) |
_Imaginary | Imaginary number type (C99) |
Tips about Keywords
Case-sensitive –
Int≠int.Cannot use as identifiers – variables, functions, structs.
Reserved for future standards – new C versions may add keywords.
Some keywords are rarely used in basic programs:
restrict,_Complex,_Imaginary.
Example Usage of Some Keywords
Summary Table by Category
| Category | Keywords |
|---|---|
| Data Types | int, char, float, double, void, short, long, signed, unsigned, _Bool, _Complex, _Imaginary |
| Control Flow | if, else, switch, case, default, for, while, do, break, continue, goto, return |
| Storage Classes | auto, register, static, extern, typedef, volatile, const |
| Derived Types | struct, union, enum |
| Operators/Other | sizeof, inline, restrict |
