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Identifiers and Keywords

4 years ago

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Each program elements in a C program are given a name called identifiers. Names given to identify Variables, functions and arrays are examples for identifiers. Keywords are pre-defined words in a C compiler.Each keyword is meant to perform a specific function in a C program

What are Identifiers?

An identifier is nothing but a name assigned to an element in a program.
Example, name of a variable, function, etc. Identifiers are the user-defined names consisting of 'C' standard character set. As the name says, identifiers are used to identify a particular element in a program. Each identifier must have a unique name. These identifier are defined against a set of rules.

Rules for an Identifier

An Identifier can only have alphanumeric characters(a-z , A-Z , 0-9) and underscore(_).
The first character of an identifier can only contain alphabet(a-z , A-Z) or underscore (_).
Identifiers are also case sensitive in C. For example name and Name are two different identifiers in C.
Keywords are not allowed to be used as Identifiers.
No special characters, such as semicolon, period, whitespaces, slash or comma are permitted to be used in or as Identifier.

What are Keywords?

In C, we have 32 keywords, which have their predefined meaning and cannot be used as a variable name. These words are also known as “reserved words”. It is good practice to avoid using these keywords as variable name.

As C is a case sensitive language, all keywords must be written in lowercase. Here is a list of all keywords allowed in ANSI C.

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

Basics usage of these keywords

Keywords	Usage
if, else, switch, case, default	Used for decision control programming structure.
int, float, char,short, double, long	These are the data types and used during variable declaration.
for, while, do	types of loop structures in C.
auto, signed, const,static, volatile,extern, register, unsigned	defines a variable.
break	Used with any loop OR switch case.
void	One of the return type
goto	Used for redirecting the flow of execution
return	This keyword is used for returning a value
continue	It is generally used with for, while and do-while loops, when compiler encounters this statement it performs the next iteration of the loop, skipping rest of the statements of current iteration.
enum	Set of constants
sizeof	It is used to know the size.
struct, typedef	Both of these keywords used in structures (Grouping of data types in a single record)
union	It is a collection of variables, which shares the same memory location and memory storage