C Keywords and Identifiers

Keywords :

Keywords are the reserve words which can not be used as variables.

These are the sytem defined variables.

C++ has many different keywords.

White spaces are not allowed in keywords.

These are in lower case.

Following table shows the common keywords present in both C and C++.

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

Identifiers :

These are the words or names which identify whether it is a constant, variable or function name in C.

It reprsent unique sequence of characters.

These must be maximum upto 31 characters long.

All the identifiers are case sensitive.

Special characters or keywords should not be used as indentifiers.

Rules in C for creating identifiers are :

Only alphabet characters, digits and underscores are permitted.

The name can't be started with digit.

The keyword can't be used as a name.

These are case sensitive.

Identifier name can't have space.

The name can't have a special character.

Example :

Following are some valid identifiers :

number, number1, x, xyz etc.

following are the Invalid identifiers :

7xy(first letter is digit), first name(has space), break(reserve word)