Yes, beefhash is correct (posting underneath to emphasise it :-)) Just one quick clarification if it's not obvious. If you don't care about other people and just want to put your code in the public domain the US (and you are in the US), a statement to that effect is enough. However, people outside the US will not be able to safely use your code. Someday if you change your mind, you can sue them. So if you care about those people you need to choose an appropriate license to offer them.
There is a good example of this that came up recently. Jason Rohrer wrote the game One Hour One Life and put it in the public domain. An unrelated group wanted to offer the game on mobile and in other markets (notably Japan). They specifically asked for his permission to do that. He agreed. As far as I know, that's enough. So it doesn't have to be complicated -- it's just a PITA for others to keep asking for permission if you don't give them a license up front.
There is a good example of this that came up recently. Jason Rohrer wrote the game One Hour One Life and put it in the public domain. An unrelated group wanted to offer the game on mobile and in other markets (notably Japan). They specifically asked for his permission to do that. He agreed. As far as I know, that's enough. So it doesn't have to be complicated -- it's just a PITA for others to keep asking for permission if you don't give them a license up front.