Constants and Variables

Constants and Variables

In this tutorial you will learn about Character Set, C Character-Set Table, Special Characters, White Space, Keywords and Identifiers, Constants, Integer Constants, Decimal Integers, Octal Integers, Hexadecimal integer, Real Constants, Single Character Constants, String Constants, Backslash Character Constants [Escape Sequences] and Variables.

Instructions in C language are formed using syntax and keywords. It is necessary to strictly follow C language Syntax rules. Any instructions that mis-matches with C language Syntax generates an error while compiling the program. All programs must confirm to rules pre-defined in C Language. Keywords as special words which are exclusively used by C language, each keyword has its own meaning and relevance hence, Keywords should not be used either as Variable or Constant names.

Character Set

The character set in C Language can be grouped into the following categories.

1. Letters
2. Digits
3. Special Characters
4. White Spaces

White Spaces are ignored by the compiler until they are a part of string constant. White Space may be used to separate words, but are strictly prohibited while using between characters of keywords or identifiers.

C Character-Set Table

Letters	Digits
Upper Case A to Z	0 to 9
Lower Case a to z	.

Special Characters

,	.Comma	&	.Ampersand
.	.Period	^	.Caret
;	.Semicolon	*	.Asterisk
:	.Colon	-	.Minus Sign
?	.Question Mark	+	.Plus Sign
'	.Aphostrophe	<	.Opening Angle (Less than sign)
"	.Quotation Marks	>	.Closing Angle (Greater than sign)
!	.Exclaimation Mark	(	.Left Parenthesis
|	.Vertical Bar	)	.Right Parenthesis
/	.Slash	[	.Left Bracket
	.Backslash	]	.Right Bracket
~	.Tilde	{	.Left Brace
-	.Underscore	}	.Right Bracket
$	.Dollar Sign	#	.Number Sign
%	.Percentage Sign	.	.

.

.
.White Space

1. Blank Space
2. Horizontal Tab
3. Carriage Return
4. New Line
5. Form Feed

Keywords and Identifiers

Every word in C language is a keyword or an identifier. Keywords in C language cannot be used as a 
variable name. They are specifically used by the compiler for its own purpose and they serve as building 
blocks of a c program.

The following are the Keyword set of C language.

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

some compilers may have additional keywords listed in C manual.

Identifiers refers to the name of user-defined variables, array and functions. A variable should be essentially
a sequence of letters and or digits and the variable name should begin with a character.

Both uppercase and lowercase letters are permitted. The underscore character is also permitted in identifiers.