Tokens in C Programming Language

What is token?

C program is basically a collection of many functions. But it has basic building blocks, these basic buildings blocks in C language which are constructed together to write a C program. This basic building blocks are called Token.

Each and every  smallest individual unit in a C program is known as C tokens.

Simply we can say that C program is also a collection of tokens, comments, and whitespaces.

In C, Programming tokens are of six types. They are,

• In C Programming punctuation, individual words, characters etc are called tokens.

• Tokens are basic building blocks of C Programming

We have learnt different type of tokens in C. In the upcoming chapters we will learn C tokens, keywords and identifiers in more details.

Keyword

Keywords are a special part of a language definition. Keywords are predefined, reserved words used in programming that have special meanings to the compiler. These meaning of the keywords has already been described to the C compiler. These meaning cannot be changed. Thus, the keywords cannot be used as variable names because that would try to change the existing meaning of the keyword, which is not allowed. Keywords are part of the syntax and they cannot be used as an identifier. But one can change these words as identifiers by changing one or more letters to upper case, How ever this will be a bad practice so we should avoid that.

C language has reserved 32 words as keywords

All the Keywords are written in lower-case letters. Since C is case-sensitive

int distance ;
int roll_mo ;
float area ;
 

Here, int, float is a keyword that indicates 'distance', 'roll_no', 'area' are a variable of type integer.

Identifiers

Identifiers are the names of variables, union, function name, structure names.

Identifier must follow some rules. Here are the rules:

• All identifiers must start with either a letter( a to z or A to Z ) or currency character($) or an underscore.
• They must not begin with a digit
• After the first character, an identifier can have any combination of characters.
• A C keywords cannot be used as an identifier.
• Identifiers in C are case sensitive, foo and Foo are two different identifiers.
• They can be any length

Each variable has a name by which it is identified in the program. It's a good idea to give your variables mnemonic names that are closely related to the values they hold. Variable names can include any alphabetic character or digit and the underscore _. The main restriction on the names you can give your variables is that they cannot contain any white space. You cannot begin a variable name with a number. It is important to note that as in C but not as in Fortran or Basic, all variable names are case-sensitive. MyVariable is not the same as myVariable. There is no limit to the length of a C variable name. The following are legal variable names:

• MyVariable
• myvariable
• MYVARIABLE
• x
• i
• _myvariable
• $myvariable
• _9pins
• andros
• ??????
• OReilly

• 
  This_is_an_insanely_long_variable_name_that_just_keeps_going_and_going_and_going_and_well_you_get_the_idea_The_line_breaks_arent_really_part_of_the_variable_name_Its_just_that_this_variable_name_is_so_ridiculously_long_that_it_won't_fit_on_the_page_I_cant_imagine_why_you_would_need_such_a_long_variable_name_but_if_you_do_you_can_have_it

The following are not legal identifiers :

• My Variable // Contains a space
• 9pins // Begins with a digit
• a+c // The plus sign is not an alphanumeric character
• testing1-2-3 // The hyphen is not an alphanumeric character
• O'Reilly // Apostrophe is not an alphanumeric character
• OReilly_&_Associates // ampersand is not an alphanumeric character

If you want to begin a variable name with a digit, prefix the name you'd like to have (e.g. 8number) with an underscore, e.g. _8number. You can also use the underscore to act like a space in long variable names.

Constants or Literals

Literals in C are sequence of characters (digits, letters and other characters) that represent constant values to be stored in variables. C specifies five major type of literals. They are below :

String

In C and C++, strings are nothing but an array of characters ended with a null character (‘\0’).This null character indicates the end of the string. Strings are always enclosed in double quotes. Whereas, a character is enclosed in single quotes in C and C++.Declarations for String:

• char string[20] = {‘g’, ’e’, ‘e’, ‘k’, ‘s’, ‘f’, ‘o’, ‘r’, ‘g’, ’e’, ‘e’, ‘k’, ‘s’, ‘\0’};

• char string[20] = "atnyla";

• char string [] = "atnyla";

Special symbol

The following special symbols are used in C having some special meaning and thus, cannot be used for some other purpose.[] () {}, ; * = #

• Brackets[]: Opening and closing brackets are used as array element reference. These indicate single and multidimensional subscripts.

• Parentheses(): These special symbols are used to indicate function calls and function parameters.

• Braces{}: These opening and ending curly braces mark the start and end of a block of code containing more than one executable statement.

• semicolon (; ): It is used to separate more than one statements like in for loop is separates initialization, condition, and increment.

• comma (,): It is an operator that essentially invokes something called an initialization list.

• an asterisk (*): It is used for mutiplication.

• assignment operator (=): It is used to assign values.

• preprocessor(#): The preprocessor is a macro processor that is used automatically by the compiler to transform your program before actual compilation.

Operators

An operator is a symbol that takes one or more arguments and operates on them to produce a result. Operators are of many types and are considered in operator chapter

There are many types of operators in C which are given below:

• Unary Operator,

• Arithmetic Operator,

• shift Operator,

• Relational Operator,

• Bitwise Operator,

• Logical Operator,

• Ternary Operator and

• Assignment Operator.