C programming language

 Rules For Declaring Variable

• The name of the variable contains letters, digits, and underscores.
• The name of the variable is case sensitive (ex Arr and arr both are different variables).
• The name of the variable does not contain any whitespace and special characters (ex #,$,%,*, etc).
• All the variable names must begin with a letter of the alphabet or an underscore(_). 
• We cannot used C keyword(ex float,double,class)as a variable name.