Syntax of Conditionals
----------------------

   A conditional in the C preprocessor begins with a "conditional
directive": `#if', `#ifdef' or `#ifndef'.  See Conditionals-Macros,
for information on `#ifdef' and `#ifndef'; only `#if' is explained here.

Menu

If: #if Directive

Basic conditionals using `#if' and `#endif'.

Else: #else Directive

Including some text if the condition fails.

Elif: #elif Directive

Testing several alternative possibilities.