I've recently started to study music theory in more depth. I was intending to score a song i had written, but i'm confused about the key signature. The chord progression is begins;

|D |D |A |A | So this is clear to me to be in the key of D, I and V are major all good...So i have put two sharps [#] i'm sure thats ok..

then the progression goes ... |C |G |A |A | is this a modulation? how is that included on the stave? C is not in the key of D... can anyone help a n00b and clear this up for me, cheers
Head like a stone, stoned like a rock.

Perhaps it's a key change?
Then it would be a I-V-vi
It's like Superman reading the teachings of Jesus. The two greatest musicians on Earth hath combined forces. I officially quit music, as it has reached it's zenith with that cover.
You write a natural sign next to the Cs in the C chord and then sharps next to C#s in the same measure.

Actually, you only need to notate the note once in each measure, as everything is assumed to be C natural until you say it's sharp again, that is, until a new measure when everything is reset.
where the key changes put a key signature (which is the new key which im guessing is C Major) and put the time signature
Sigs Are For Pussies
i dont think the new key is C tho, because the A is not minor...
Head like a stone, stoned like a rock.