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

#include <stdio.h>

int main() {
const int max = 10; // const keyword
int i;

for(i = 0; i < max; i++) { // for keyword
if(i % 2 == 0) { // if keyword
continue; // continue keyword
}
printf("%d\n", i);
}

return 0; // return keyword
}

#include <stdio.h>

int main() {

const int max = 10; // const keyword

int i;

for(i = 0; i < max; i++) { // for keyword

if(i % 2 == 0) { // if keyword

continue; // continue keyword

}

printf("%d\n", i);

}

return 0; // return keyword

}

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`

C Keywords Reference

C Keywords Reference

List of C Keywords (C99 Standard)

Tips about Keywords

Example Usage of Some Keywords

Summary Table by Category

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