- Use only allowable characters (for C++ the first character alphabetic or underscore, can continue with alphanumeric or underscore)
- Can't use reserved words
- Length limit
These attributes vary from one programming language to another. The allowable characters and reserved words will be different. The length limit refers to how many characters are allowed in an identifier name and often is compiler dependent and may vary from compiler to compiler for the same language. However, all programming languages have these three technical rules.