[nice_byte]

You mean if we write

if (some_constant_expression) { //...code... }

and some_constant_expression evaluates to false, the entire code block will be stripped from the result?

That may be true, but it's not standardized behavior, is it?

[JoeAltmaier]

True for many compilers for many years. Its a way to integrate 'conditional compilation' into the normal program flow. It can make the code easier (or harder) to read. Use judiciously.