Preprocessor directives, such as #define and #ifdef , are typically used to make source programs easy to change and easy to compile in different execution environments. Directives in the source file tell the preprocessor to take specific actions. ... Preprocessor lines are recognized and carried out before macro expansion.

What is use of preprocessor directives in C?

Description. The preprocessor will process directives that are inserted into the C source code. These directives allow additional actions to be taken on the C source code before it is compiled into object code. Directives are not part of the C language itself.

What is the purpose of a preprocessor?

In computer science, a preprocessor (or precompiler) is a program that processes its input data to produce output that is used as input to another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers.