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.