Basically what we are all saying is that it's not going to make the program crash at first, but if you develope a decent program, higher the risk it'll crash...and you'll spend countless hours trying to figure out why, and all that because you didn't use your memory correctly.
Originally posted by Zach L.
As everyone has said, its undefined. If that snippet of code is all your program is, then chances are, the program will never actually use that block of memory, so you can (read: should not) do whatever to it without a crash. As your program grows in complexity, however, the chances that you'll actually overwrite and corrupt something that is vital to the program's execution increase significantly. If you do corrupt a part of the stack, then most likely, your program will crash.