How to name a variable

Before declaring a variable keep the following things in mind

1. The name of the variable shouldn't increase 31 characters in length. For example if you create a variable like
   int abcdefghijklmnopqrstuvwxyz123456;
   the compiler will flash an error since the length is exceeding 31 characters.
2. The first character of any variable must be an alphabet or underscore(Shift + Hyphenation). The following declaration therefore is invalid
   int 1abc;
   int #incorrect;
   while the following is correct
   int marks,int data,int _message;
3. Variable names must not contain a space or any other symbol except underscore.
4. Variable names are case sensitive. Variable name,Name,NAME,nAme are treated as different.
5. Names must be unique. Once you have used a variable name you can not use it again.
6. You can not use a keyword as a variable name, for example keywords like void,int,main have a special meaning in C therefore the names must be userdefined.
   Invalid variable names
   1. auto
   2. enum
   3. int
   4. return
   5. switch etc.