Isn't it true that initializing a variable without setting a value sets its value to NULL, not zero? If that's true, then there may be a very minor bug in Serial.print() that converts the value to zero when it's actually NULL. I haven't come across any situations where I needed a variable to be NULL in the Arduino world, but in programming in general it's very common.
In the case of an Arduino loop, NULL is probably valid but the condition is immediately false so the loop exits. Arithmetic may not compute, so the work you're doing is rendering no output or result(?)