Queen's Gambit - Responding to Unusualy Moves by Black

Recently when playing the Queen's Gambit, I've come across some strange moves played against me, shown below.  For the first diagram, with the knight on c6, how am I supposed to exploit this?  I've always heard "Don't block your c-pawn with your knight", but how should I continue on in the game?  Could someone give an example with the strongest continuation?  I guess the thing that always bugged me in my mind when seeing this was dxc, followed by Nxd4, so I'm guessing I should first play something like e3, which addresses both of those, but then what?

Then in the second diagram, the way I have played this was a3, letting black trade his best minor piece so he can "double" my pawns, but what if he just retreats the bishop?  Continue like normal?  Also, is Qa4+ a good/better move here, forcing Nc6?  Thanks for any feedback that you give.

EDIT:  What a horrible typo in the title, wow.

I am not a QGD expert, but have had great success in both the senarios.  The first example, I normally roll Nf3 or e3.  The computer half the time tells me e3 is a mistake and e4 is better, but I sort of like that pawns structure and it never takes much off for having it.  Second example = who cares right now?  The pawn takes and it is over.

black needs to eventually get some play going of his own on the Cfile in the QDG.. a pawn on c6 is a good start to hold the center, and then eventually the ...c5 counterthrust . as Chernev says, if this doesnt happen "black is doomed" I would recommend reading his book, its loaded with QGDs

I don't know if it's good or not, but I have an old game of mine on file where my opponent played 3. ... Bb4. The game continued 4. a3 Bxc3+ 5. bxc3, and I eventually won with a pawn majority thanks to my stronger pawn center. If black exchanges pieces here, he's surrendering the bishop pair, and if not, he's wasting a tempo. The doubled pawns don't matter one bit because black can't prevent cxd4 later on. And if he retreats to a5, his bishop is trapped with b4 and c5.

My favorite opening :D

1. d4 d5 2. c4 e6 3. Nc3 Bb4

the next u should do is  cxd5 ( in my opinion)

In the second position, you can play 4.e3 and 5.a3 prompting the bishop to take on c3.

Look at Nimzo-Indian games starting with : 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.e3 d5 5.a3 Bxc3 6.bxc3, when the same pawn structure arises, and especially games played by Botvinnik for model plans.