Statements that start with # in C/C++ are known as preprocessor directives, that is, they are executed before compilation begins. OP has used a #define which will replace any instance of A (IF(x)) with B (while (x)) in the code.
So the IF statement is really just a while statement.
They used a macro to make 'IF' (which is distinctly not 'if') map to 'while'. So it's really a while(1) loop, which will repeat forever, or until the program is terminated, whichever comes first.
Is this something needed "for the meme" or something with this macro or C/C++? Or why the case-sensitivity here? I only know languages like Java, Python, JS. Unfortunately the ancient tongue is not known to me.
Your point about it not running when there is nothing to iterate over is incorrect. The else-statement runs when the iterator is exhausted; if the iterator empty, it is exhausted immediately and the else-statement is executed.