The following is a preprocessor directive that can be used in C++ programs besides
many more.
The
#define directive
For example
#define PI 3.14
This statement defines macro templates. During preprocessing, the preprocessor replaces
every occurrence of PI (identifier) with 3.14 (substitute value). Here, PI is a macro tem-
plate and 3.14 is its macro expansion. The macro templates are generally declared with
capital letters for quick identification. One can also define macros with small letters. The
macro templates and its expansions must be separated with at least one blank space. It is
not necessary to provide space between # and define ...
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