b. Variables and Keywords

What is Keyword in C programming language?

In C programming language a predefined set of reserved words which provide computed control of various functions and declares in C compiler pre-processing libraries which perform special functions. The basic instructions are built up using a reserved set of words, for example main, for, if, else, switch, while, default, double, extern, for, and int, etc., Programming language C demands that they are used only for giving commands or making statements. Programmer cannot use default, for example, as the name of a variable. An attempt to do so will result in a compilation error.

In formal keywords are standard forms of identifiers that have standard predefined meaning in C compiler. Keywords are all lowercase, since uppercase and lowercase characters are not equivalent because C programming supports Case sensitivity, So it’s possible to utilize an uppercase keyword as an identifier but it’s not a good programming practice.


  1. Keywords are the words whose meaning has already been explained to the C compiler and their meanings cannot be changed. Hence keywords are also called ‘Reserved words’.
  2. Keywords can be used only for their intended purpose.
  3. Keywords serve as basic building blocks for program statements.
  4. Keywords can’t be used as programmer defined identifier.
  5. The keywords can’t be used as names for variables.
  6. All keywords must be written in lowercase.
  7. 32 keywords available in C.

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