Why is the using statement required for StreamWriter(not the System.IO declaration)?

[Smashbrosboy]

Why does this code not write anything (System.IO was already declared in the code earlier for both)...

string selection = "initialsave";
        StreamWriter sw = new StreamWriter("C:\\Program Files\\BattleGame\\" + selection + ".txt");
        sw.WriteLine("testtesttest");

and why does this code actually write what was told to be written?

string selection = "initialsave";
        using (StreamWriter sw = new StreamWriter("C:\\Program Files\\BattleGame\\" + selection + ".txt"));
{
        sw.WriteLine("testtesttest");
}

I was writing a game and constantly wondering why my game was never saving. I checked the game and I found that the save files were created but not written to. Why is this?

[QuackWare]

If you don't use the "using" you have to call sw.Close() or else it wont save.