C Identifiers (Variable Names)

C Identifiers (Variable Names)

Every name you invent in C is called an identifier. There are rules about what counts as a valid one.

The naming rules

An identifier must follow these laws:

• Can use letters (a-z, A-Z), digits (0-9), and the underscore _.
• Cannot start with a digit. 1value is illegal; value1 is fine.
• Cannot contain spaces or most punctuation (-, +, ?, etc.).
• Cannot be a keyword of the language (like int, if, return).
• Case-sensitive: Score and score are two different names.

Valid vs invalid

int myNumber;      // good
int _temp;         // good (though leading _ has special rules)
int value2;        // good
int 2value;        // BAD: starts with a digit
int my-number;     // BAD: dash is not allowed
int int;           // BAD: int is a keyword

Best practices

• Use descriptive names that say what the variable holds: maxSpeed, not m.
• Use snake_case for multi-word names: player_health.
• Be consistent - pick a style and keep it.

Reserved keywords

A keyword is a word the language keeps for itself. Some examples:

int, if, else, for, while, return, void, const, break, case

TL;DR

• Identifiers use letters, digits, and _; they can't start with a digit.
• No spaces, no punctuation like -, no keywords.
• C is case-sensitive: Score != score.
• Prefer clear, descriptive, consistent names.