Keywords in C

Keywords are predefined (reserved) words in C that have special meaning to the compiler.

They are part of the language syntax
They cannot be used as identifiers (variable, function, or struct names)

List of Keywords in C

auto	break	case	char	const	continue	default	do
double	else	enum	extern	float	for	goto	if
int	long	register	return	short	signed	sizeof	static
struct	switch	typedef	union	unsigned	void	volatile	while

We cannot use these keywords as identifiers (such as variable names, function names, or struct names). The compiler will throw an error if we try to do so.

Example: The code below demonstrates what happens when we use a keyword as a variable name:

#include <stdio.h>

int main() {
    int return = 10;   
    printf("%d\n", return);
    return 0;
}

Output

error: expected identifier before 'return'

Let's categorize all keywords based on context for a more clear understanding.

Category	Keywords
Data Type Keywords	char, int, float, double, void, short, long, signed, unsigned
Operator & Utility Keywords	sizeof, return, goto, typedef
Control Flow Keywords	if, else, switch, case, default, for, while, do, break, continue
Storage Class Keywords	auto, register, static, extern
Type Qualifiers	const, volatile
User Defined Types	struct, union, enum

Read about Differences between Keywords and Identifiers in C.

List of Keywords in C

Explore