Another bug

Because I've already established examiners love problem-solving abilities, I'll post another problem. I tried to add a function that will work out whether or not a player is in check after the opponent makes their move, but what it does is constantly tell everyone they're in check, after every single move. So I'll fix it and then edit this post to explain how I fixed it. I hate posting mundane stuff like this.

EDIT:
Well, here's what the problem was. As I might have explained somewhere else on the blog, each different chess piece is represented by a number, 1 being a pawn, 2 being a rook, etc. Positive number are white pieces, negative numbers are black pieces (-1 is a black pawn, 1 is a white pawn). To work out whether the king was in check, I traced outwards from the king, looking for certain pieces in certain directions (i.e. bishops or queens diagonally). In the check for these pieces, I compared the absolute value of the piece to the pieces I was looking for, because it required less thought than trying to work out the correct sign. That is, if I was looking for a bishop diagonally, I'd check in all diagonal directions whether the absolute value of the piece was 4 (the bishop's number). Stupidly enough, I didn't realise this would also include piece's that belonged to the player, along with the opponent's pieces. So basically, each player's queen kept putting that player in to check.