What is the purpose of pre-processing in the C language?

The C language preprocessor is a part of the C language compiler, primarily used to preprocess source code, with functions including:

1. Macro definition and macro replacement: The preprocessor can define macros and use them to replace in the source code, which can improve the maintainability and readability of the code.
2. This file includes: Preprocessor can use the #include directive to include content from other files into the current source file, making it easy to organize and reuse code.
3. Conditional compilation allows preprocessors to control whether certain code segments are included in the compilation process based on conditional compilation directives such as #ifdef, #ifndef, #if, #elif, #else, and #endif.
4. Line control: The preprocessor can change the compiler’s output line numbers and file names using the #line directive, which can help developers track code during debugging.

In general, the C language preprocessor is mainly used to preprocess source code in order to perform necessary operations on the source code during compilation, resulting in executable target code.