Identifiers are names given to different entities such as constants, variables, structures, functions, etc.
int amount; double totalbalance;
In the above example, amount and totalbalance are identifiers and int, and double are keywords.
Rules for Naming Identifiers
- An identifier can only have alphanumeric characters (a-z , A-Z , 0-9) (i.e. letters & digits) and underscore( _ ) symbol.
- Identifier names must be unique
- The first character must be an alphabet or underscore.
- You cannot use a keyword as identifiers.
- Only the first thirty-one (31) characters are significant.
- It must not contain white spaces.
- Identifiers are case-sensitive.
Identifiers in C - Video Tutorial
To understand "C Identifiers" in more depth, please watch this