In `double A[5];`, `A` is an identifier: a name for a program entity. In `int main(void)`, `main` names a function. Identifiers also name type aliases, such as `size_t`, and constants, such as `EXIT_SUCCESS`. Unlike a literal such as `5`, an identifier refers to something whose properties must be established. section 2.1 section 2.2
Before using an identifier, give the compiler a declaration that says what it represents. Keywords are different: the language predefines them, and they must not be declared or redefined. TAKEAWAY: All identifiers in a program have to be declared. section 2.2
Read a declaration from the name outward
In `int argc;`, `argc` names an `int` object. In `double A[5];`, brackets mark `A` as an array of five `double` items. In `int main(int, char*[]);`, parentheses mark `main` as a function returning `int`. A declaration establishes these properties; a definition additionally specifies how and where an object or function comes to be. section 2.2 section 2.5
Names also affect readability. The standard-library type name `size_t` uses a trailing `_t` as a naming convention for types. Variable, function, and type names should make code accessible to its readers; a project's natural language and domain terminology can guide that choice. section 2.1 section 9.4
long année = 1990L; // Année de l'écriture de l'œuvre
`année` illustrates a non-Latin character in a C identifier, while the comment uses the same language for documentation. C23 clarifies allowed identifiers by referring to Unicode UAX #31; earlier standards permitted many such characters in principle, but their rules and tooling made use difficult. section 9.3
