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C Programming Language - 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
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Letters
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Digits
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Upper Case A to Z
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0 to 9
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Lower Case a to z
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. |
Special Characters
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,
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.Comma
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&
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.Ampersand
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.
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.Period
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^
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.Caret |
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;
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.Semicolon
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*
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.Asterisk
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:
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.Colon
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-
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.Minus Sign
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?
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.Question Mark
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+
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.Plus Sign
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'
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.Aphostrophe
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<
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.Opening Angle (Less than sign)
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"
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.Quotation Marks
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>
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.Closing Angle (Greater than sign)
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!
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.Exclaimation Mark
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(
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.Left Parenthesis
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|
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.Vertical Bar
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)
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.Right Parenthesis
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/
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.Slash
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[
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.Left Bracket
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\
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.Backslash
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]
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.Right Bracket
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~
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.Tilde
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{
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.Left Brace
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-
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.Underscore
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}
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.Right Bracket
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$
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.Dollar Sign
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#
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.Number Sign
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%
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.Percentage Sign |
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. |
.
.
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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.
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