Macros

A macro, defined with #define, is a preprocessor directive that gives a name to a piece of code, which is then substituted wherever that name appears before compilation. Macros can be simple constants, like #define PI 3.14159, or function-like, taking parameters and expanding into a code pattern. Because macro expansion is purely textual, careless macros without proper parentheses around their parameters can produce surprising results when combined with other operators.