The preprocessor is a simple macro processor that processes the source text of a C program before the program is read by the compiler. It is controlled via single-line preprocessor directives and transforms the original source text by interpreting macros embedded in the original source text to substitute, add, or remove text based on the given directives. The resulting preprocessed source text must then be a valid C program.
The following table provides an overview of the basic preprocessor directives:
| #include | Insert text from another source file. |
| #define | Add a preprocessor macro definition. |
| #undef | Remove a preprocessor macro definition. |
