Variables in c programming

    Topics:

    1.Character Set :-
    2.C Tokens :-

• Keywords & Identifiers 
• Constants 
• Integer
• Floating Point
• Character, String
• Enumeration 

     3. Backslash characters / Escape sequences 

      1.Character Set:

2. C tokens:

•     Smallest individual units is called as ‘Tokens‘.

     

• Keywords And Identifiers:

• Every C word is classified either “Keyword” or “Identifier “. 

      Rules for Keywords:

•          Has fixed meaning 
•          Meaning can not be changed 
•          Served as basic building block for program statement. 
•          Must be written in lower case

Identifiers:

-Refer to names of variables , functions and arrays .

Rules for identifiers:

1.     First character must be an alphabet (or underscore) 

2.     Must consist of only letters, digits or underscore. 

3.     Only first 31 characters are significant. 

4.     Cannot use a keyword

5.     Must not contain white space

Constants:

Constants in C refers to fixed values and do not change during the execution of a program.

• Integer Constants 
• Real Constants can be represented as exponential format. mantissa e exponent 
• Mantissa is either a real number expressed in decimal notation or integer 
• The exponent is an integer number with an optional plus or minus sign 
• The letter e can be written in lowercase or uppercase.
• Single character constants 
• String constants 
• Backslash Character constants – useful in output functions  also known as escape sequences.

Escape sequence:

Variables:

• A data name used to store data values
•  May take different values at different times of program execution 

• Rules for variable :

 1.      Should not be keyword 

 2.      Should not contain white space

 3.      Uppercase and lower case are significant

 4.      Must begin with letter ( or underscore) 

 5.      Normally should not be more than eight characters.