The alphabets,digits,symbols when properly combined forms constants,variables and keywords.
Constants do not change whereas variables can be changed.
Variables are used to store data.It’s value can be changed and can be reused many times.
Rule to name Variables and Constants:
The first character of a variable or constant name must be an alphabet or underscore.
Variable or constant names can have alphabets,digits or underscores.
No commas or blanks are allowed within a name of variable or constant.
No special symbol other than underscore can be used.
Variable or constant name must not be any reserved word i.e keyword.
Keywords are the reserved words i.e the words whose meaning has already been explained to the computer.
These keywords cannot be used as variable or constant names because if we do so we are trying to assign a new meaning to the keyword,which is not allowed.
Declaration of Variables in C:
C compiler makes it compulsory to declare the types of any variable name that you wish to use in your code.This type declaration is done at the beginning of the program.