C Tokens, Keywords, Identifiers

Details

What is a Character set?

Like every other language, 'C' also has its own character set. A program is a set of instructions that, when executed, generate an output. The data that is processed by a program consists of various characters and symbols. The output generated is also a combination of characters and symbols.

A character set in 'C' is divided into,

A compiler always ignores the use of characters, but it is widely used for formatting the data. Following is the character set in 'C' programming:

  1. Letters
    • Uppercase characters (A-Z)
    • Lowercase characters (a-z)
  2. Numbers
    • All the digits from 0 to 9
  3. White spaces
    • Blank space
    • New line
    • Carriage return
    • Horizontal tab
  4. Special characters
    • Special characters in 'C' are shown in the given table,
, (comma) { (opening curly bracket)
. (period) } (closing curly bracket)
; (semi-colon) [ (left bracket)
: (colon) ] (right bracket)
? (question mark) ( (opening left parenthesis)
' (apostrophe) ) (closing right parenthesis)
" (double quotation mark) & (ampersand)
! (exclamation mark) ^ (caret)
|(vertical bar) + (addition)
/ (forward slash) - (subtraction)
\ (backward slash) * (multiplication)
~ (tilde) / (division)
_ (underscore) > (greater than or closing angle bracket)
$ (dollar sign) < (less than or opening angle bracket)
% (percentage sign) # (hash sign)

What is Token in C?

TOKEN is the smallest unit in a 'C' program. It is each and every word and punctuation that you come across in your C program. The compiler breaks a program into the smallest possible units (tokens) and proceeds to the various stages of the compilation. A token is divided into six different types, viz, Keywords, Operators, Strings, Constants, Special Characters, and Identifiers.

Tokens in C

Keywords and Identifiers

In 'C' every word can be either a keyword or an identifier.

Keywords have fixed meanings, and the meaning cannot be changed. They act as a building block of a 'C' program. There are a total of 32 keywords in 'C'. Keywords are written in lowercase letters.

Following table represents the keywords in 'C'-

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

An identifier is nothing but a name assigned to an element in a program. Example, name of a variable, function, etc. Identifiers are the user-defined names consisting of 'C' standard character set. As the name says, identifiers are used to identify a particular element in a program. Each identifier must have a unique name. Following rules must be followed for identifiers:

  1. The first character must always be an alphabet or an underscore.
  2. It should be formed using only letters, numbers, or underscore.
  3. A keyword cannot be used as an identifier.
  4. It should not contain any whitespace character.
  5. The name must be meaningful.

Summary

 

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