Was macdonwald was a member of duncan's army

(You are talking about Macbeth, yes?)

MacDonald doesn't technically appear in the play, but he's mentioned in Act 1, Scene 2. MacDonald was the former Thane of Cawdor; and no, he wasn't a member of Duncan's Army. He was a traitor who fought for the Norwegians. However, Duncan didn't know this, and during the battle it was discovered that MacDonald was a traitor. Read the Captain's first paragraph in Act 1, Scene 2 if you need more information.