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Tuesday, 16 May 2017 06:10

Keywords and Identifiers

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In this tutorial, you will learn about keywords; reserved words in C programming that are part of the syntax. Also, you will learn about identifiers and proper way to name a variable.

Character set

Character set is a set of alphabets, letters and some special characters that are valid in C language.


Uppercase: A B C ................................... X Y Z
Lowercase: a b c ...................................... x y z

C accepts both lowercase and uppercase alphabets as variables and functions.



0 1 2 3 4 5 6 7 8 9

Special Characters

Special Characters in C Programming
, < > . _
( ) ; $ :
% [ ] # ?
' & { } "
^ ! * / |
- \ ~ +  

White space Characters

blank space, new line, horizontal tab, carriage return and form feed

C Keywords

Keywords are predefined, reserved words used in programming that have special meanings to the compiler. Keywords are part of the syntax and they cannot be used as an identifier. For example:

int money;



Here, int is a keyword that indicates 'money' is a variable of type integer. 

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.

Keywords in C Language
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

Along with these keywords, C supports other numerous keywords depending upon the compiler.

C Identifiers

Identifier refers to name given to entities such as variables, functions, structures etc.

Identifier must be unique. They are created to give unique name to a entity to identify it during the execution of the program. For example:

int money;
double accountBalance;

Here, money and accountBalance are identifiers.

Also remember, identifier names must be different from keywords. You cannot use int as an identifier because int is a keyword.

Rules for writing an identifier

  1. A valid identifier can have letters (both uppercase and lowercase letters), digits and underscores.
  2. The first letter of an identifier should be either a letter or an underscore. However, it is discouraged to start an identifier name with an underscore.
  3. There is no rule on length of an identifier. However, the first 31 characters of identifiers are discriminated by the compiler.

Good Programming Practice

You can choose any name for an identifier (excluding keywords). However, if you give meaningful name to an identifier, it will be easy to understand and work on for you and your fellow programmers.

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