Conditional compilation - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is conditional compilation in C?

Conditional compilation allows the compiler to include or exclude parts of the code based on certain conditions, usually using preprocessor directives like #if, #ifdef, and #ifndef.

beginner

What does the #ifdef directive do?

#ifdef checks if a macro is defined. If it is, the code following it up to #endif is included in compilation.

beginner

How do you exclude code when a macro is defined?

Use #ifndef MACRO_NAME to include code only if the macro is NOT defined.

beginner

What is the purpose of #else in conditional compilation?

#else provides an alternative block of code to compile if the condition in #if or #ifdef is false.

intermediate

Give an example of conditional compilation to compile code only on Windows.

Example:<br>

#ifdef _WIN32
// Windows-specific code
#endif

This compiles the code inside only if _WIN32 is defined, which usually means the program is being compiled on Windows.

Which directive checks if a macro is NOT defined?

A #else

B #ifndef

C #if

D #ifdef

#ifndef means "if not defined" and includes code only if the macro is not defined.

What happens to code inside #ifdef MACRO if MACRO is not defined?

A It is excluded from compilation

B It is always compiled

C It causes a compilation error

D It is compiled twice

If the macro is not defined, the code inside #ifdef is skipped.

Which directive can be used to provide an alternative code block if a condition is false?

A #include

B #endif

C #define

D #else

#else is used to specify code that compiles when the #if or #ifdef condition is false.

What is the role of #endif in conditional compilation?

A It includes a file

B It defines a macro

C It ends a conditional directive block

D It comments out code

#endif marks the end of a conditional compilation block started by #if, #ifdef, or #ifndef.

Which directive would you use to check a condition with a value, not just if a macro is defined?

A #if

B #ifdef

C #ifndef

D #else

#if allows checking expressions or values, unlike #ifdef which only checks if a macro is defined.

Explain how conditional compilation helps in writing cross-platform C programs.

Think about how you can write code that works on Windows and Linux by including only the right parts.

Describe the difference between #ifdef and #if directives.

One checks presence, the other checks a condition.