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 does preprocessor directives do in C?

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.

What is preprocessor directive give an example?

Examples of some preprocessor directives are: #include, #define, #ifndef etc. Remember that # symbol only provides a path that it will go to the preprocessor, and command such as include is processed by preprocessor program. For example, include will include extra code to your program.