A string is an array of chars THAT IS NULL TERMINATED.
Just because you have an array that contains characters is not enough to make it a string. The NULL terminator is required.
Rob's code is correct in that it does add a NULL terminator, before expecting it to be used as a string, but I don't like it because the array is not always a string, so you can't print it as a string at any time. I prefer, and it doesn't take that much extra time, to always add a NULL after each character, so that the char array is always a string.