Such thing does exist, and you should know it if you are using this language:
Honestly, you could much better use your time if you simply read a language manual before trying to write a program and just used a reference (MSDN, apparently, provides all that), instead of asking such questions.
Also, you don't understand it right. Just think about it: those default values are known during compilation; there is no such thing as "defining constants at call time", otherwise you could not call them "constant". This is not the case even in your own example — they are normal constants. Apparently, constant expression are also allowed (because there are no reason not to have them: the compiler can always evaluate constant expressions).