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IDENTIFIERS AND KEYWORDS

IDENTIFIER: ldentzfiers are names that are given to various program elements, such as variables, functions and arrays.Identifiers consist of letters and digits, in any order, except that the first character must be a letter. Both upper- and lowercase letters are permitted, though common usage favors the use of lowercase letters for most types of identifiers. Upper- and lowercase letters are not interchangeable . The underscore character ( - ) can also be included, and is considered to be a letter. An underscore is often used in the middle of an identifier. An identifier may also begin with an underscore, though this is rarely done in practice.An identifier can be arbitrarily long. Some implementations of C recognize only the first eight characters, though most implementations recognize more (typically, 3 1 characters). Additional characters are carried along for the programmer's convenience. 



Some Valid Identifier:

1.   X 
2.   Y
3.   sum
4.   name
5.   area
6.    mouse 
7.   nano etc 
keyword:There are certain reserved words, called keywords, that have standard, predefined meanings in C. These
keywords can be used only for their intended purpose; they cannot be used as programmer-defined identifiers.


The standard keywords are:


1.   auto 
2.   extern
3.   sizeof
4.   break
5.   f l o a t n s t a t i c
6.   case 
7.   f o r s t r u c t
8.   char
9.   got0
10.       switch
11.       const
12.       i f 
13.       typedef
14.       continue
15.       i n t
16.       union
17.       d e f a u l t I 
18.       long
19.       unsigned
20.       do
21.       r e g i s t e r 
22.       void
23.       double
24.       return
25.       v o l a t i l e
26.       else
27.       short
28.       while
29.       enum 
30.       signed

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