TIL, as they say. This is completely valid C++ code, compiling without any errors.
#include <iostream> int main() <% int a<:5:> = <% 1, 2, 3, 4, 5 %>; std::cout << a<:2:>; return 0; %>
It all has to do with so called di- and trigraphs. Of course I would not use these anywhere unless, somehow, absolutely necessary. No doubt it would only get people confused about your code.