A constant is a fixed value bound to an identifier. These may aid readability and maintainability (i.e. avoiding magic literals) and may also act as a means to provide an addressable flag (i.e. defining a constant in support of conditional declaration).
Depending on the language constants may be expanded at compile time, such that the resulting program text only includes the value rather than the identifier. In other cases “constant” here would correspond to a statically adressable immutable value (that could for instance be subsequently inlined).
This does not include immutable bindings that may vary across contexts (i.e. any kind of “constant” tied to a given function invocation), nor does it apply to references/pointers which are not conducive to inlining. These are all valuable tools but are distinct concepts and conflating them may intoduce runtime surprises due to the potentially different times of expansion (i.e. linking against a previously compiled unit may result in value dissonascence).
The #define preprocessor directive can be used for
constant definition which will result in replacement in the source prior
to compilation.
#define CONSTANT_NAME <value>The #define preprocessor directive can be used for
constant definition which will result in replacement in the source prior
to compilation.
#define CONSTANT_NAME <value>