Every language has some basic elements and grammatical rules. These
basic elements are character set, variables, datatypes, constants, keywords,
variable declaration, expressions, statements etc,. all of these are used to
construct a c program.
2.1 Character set:
Upper and lower case
A,B,C,D,……..Z
A,b,c,d,………z
Digits
1,2,3,4,….
Graphic Characters
White space characters
Space
character, neline character, horizontal tab, vertical tab, and form feed.
Other characters
Alert, backspace,
carriage return, and null character.
2.2 Escape sequence/ Execution characters:
C supports combination of backslash ( \ ) and some characters from the C
character for representing these characters in our C programs. These characters
are known as escape sequences.
2.3 Delimiters
These are used for syntactic purpose in C
: colon used for label
; semicolon end of statement
() parentheses used in expression
[] square brackets used for arrays
{} curley braces used for block of statements
# hash preprocessor
directive
, comma variable delimiter
2.4 Keywords:
Keywords are the vocabulary of
C. Because they are special to C, you can't use them as identifiers, for example, or
as variable names. Many of these keywords specify various types, such as int. Others,
such as if, are used to control the order in which program
statements are executed. These are always written in lowercase. There are only
32 keywords available
auto break case char const continue default do double else
enum extern float for goto if int long register return
short
short
2.5 Identifiers :
All the words that we will use in our c program will be either keywords
or identifiers. Keywords are predefined and can’t be changed by the user, while
identifiers are user defined words and are used to give names to entities like
variables, arrays, functions, structures etc., Rules for naming identifiers are
Rule 1: the name should consist of UPPERCASE, lowercase, digits and underscore(_).
Rule 2: First character should be alphabet or underscore.
Rule 3: The name should not be a keyword.
Rule 4: C is a case sensitive, the lowercase and uppercase letters are
different.
Rule 5: Some implementations of C recognize only the first eight
characters, though most implementations recognize 31 characters.
Examples of valid Identifiers are :
Temp a _initial data_type Marks Percent
Invalid identifiers are:
5abd int rec# avg.no high num(space not allowed)
Keep in mind all these rules before using identifier.