Final answer:
The correct purpose of a pre-processor directive is to include external libraries and handle conditional compilation, typically in C or C++ programming. Examples include using #include to import libraries and #ifdef for conditional compilation blocks.
Step-by-step explanation:
Pre-processor directives in programming are special instructions that are interpreted by the pre-processor before actual compilation starts. They are not part of the program itself, but rather commands to the compiler's pre-processor. Two common purposes of pre-processor directives include:
- Including external libraries - This is done with the #include directive, which allows the programmer to import the content of one file into another. For example, #include <iostream> in C++ includes the input-output stream library which is necessary for tasks such as printing to the console.
- Handling conditional compilation - The #ifdef, #ifndef, #endif, #if, #else, and #elif directives allow code to be compiled only if certain conditions are met. For instance, #ifdef DEBUG could wrap debugging code that only compiles if the DEBUG symbol has been previously defined.
The incorrect options are:
- A) Inserting comments in the code is not performed by pre-processor directives; comments are simply ignored by the compiler.
- B) Pre-processor directives do not perform mathematical calculations; arithmetic is handled during execution, not at compile-time.
- D) Declaring variables is done in the actual code; the pre-processor does not handle variable declarations.