Check and checkmate implemented.

After a lot of bugs, I've finally implemented check and checkmate in to my program. So now, a player can't move in to check, a player has to move out of check, and checkmate can be detected, and will end the game.

I also tidied up the code a fair bit, it's very easy for subroutines to get out of hand on a project like this.

And pawn promotion is done. Although you can only promote a pawn to a queen, but it's just not worth implementing pawn promotion to any piece.

One strange little glitch I'm having is when a game is won and the board is reset, a seemingly random piece appears on the square shown in the picture. How peculiar.

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.

Glitches

Some strange glitches are occurring whilst I'm playing my chess game involving the computer's moves. The computer attempted to take my pawn with its bishop, but his bishop disappeared. Later, it attempted to move a queen, and the queen disappeared. I'm posting this because it will hopefully demonstrate my problem-solving abilities. Examiners love problem-solving abilities.

EDIT:
I fixed the problem. Turns out where I wrote 39 and 89 in two lines should have been 38 and 88. Obviously. Here's a picture, in case you're unsure as to what those numbers look like.

It plays!

I've gotten to the point where you can actually play against the computer now. It does, for now, pick its moves randomly, and there is, for now, no way of detecting check or checkmate, but at least it plays.

(Obligatory picture which looks the same as all previous pictures):

A flowchart

This is a flowchart that I have used to determine what to do when a square on the board is clicked by the user.

DISCLAIMER: This was not posted because I felt I really needed to post something soon because I haven't posted anything for a while. This is definitely actual work.