Rules and Naming Convention for Variables and constants

1. Constant and variable names should have a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore (_). For example:

   snake_case
   MACRO_CASE
   camelCase
   CapWords

2. Create a name that makes sense. For example, vowel makes more sense than v.
3. If you want to create a variable name having two words, use underscore to separate them. For example:

   my_name
   current_salary

4. Use capital letters possible to declare a constant. For example:

   PI
   G
   MASS
   SPEED_OF_LIGHT
   TEMP

5. Never use special symbols like !, @, #, $, %, etc.
6. Don't start a variable name with a digit.