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4.2.4 Else

The `#else' directive can be added to a conditional to provide alternative text to be used if the condition fails. This is what it looks like:

     #if expression
     #else /* Not expression */
     #endif /* Not expression */

If expression is nonzero, the text-if-true is included and the text-if-false is skipped. If expression is zero, the opposite happens.

You can use `#else' with `#ifdef' and `#ifndef', too.