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110i

121

playingfalseplayingfalseX's turn?

available squaresavailable squares1

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gQmCqggKfyOpwAgWwB6Qk8FlDAj218Q4AAAQIEpgko4Gm0DiZAgEC2gPTPBRTwcx/fEiBAgACBKQIKeAqrQwkQIEAgW+B1egX82sgTBAgQIEBguIACHk7qQAIECBAg8Fpg5wJ+nd4TBAgQIECgSEABF8G7lgABAgSyBRTwrvuXiwABAgSWFlDAS6/HcAQIECCwq4AC3nWz2bmkJ0CAwPICCnj5FRmQAAECBHYUUMA7blWmbAHpCRBoIaCAW6zJkAQIECCwm4AC3m2j8hDIFpCeQBsBBdxmVQYlQIAAgZ0EFPBO25SFAIFsAelbCSjgVusyLAECBAjsIqCAd9mkHAQIEMgWaJdeAbdbmYEJECBAYAcBBbzDFmUgQIAAgXYCQwu4XXoDEyBAgACBIgEFXATvWgIECBDIFlDAw/bvIAIECBAg8L6AAn7fypMECBAgQGCYgAIeRpl9kPQECBAgcExAAR/z8jQBAgQIEBgioICHMDokW0B6AgQIHBdQwMfNvEGAAAECBC4LKODLhA4gkC0gPQECv+uE6gAAAkNJREFU5wQU8Dk3bxEgQIAAgUsCCvgSn5cJEMgWkJ7AeQEFfN7OmwQIECBA4LSAAj5N50UCBAhkC0h/TUABX/PzNgECBAgQOCWggE+xeYkAAQIEsgWup1fA1w2dQIAAAQIEDgso4MNkXiBAgAABAtcFOhfw9fROIECAAAECRQIKuAjetQQIECCQLaCAu+7f3AQIECDQWkABt16f4QkQIECgq4AC7rq57LmlJ0CAQHsBBdx+hQIQIECAQEcBBdxxa2bOFpCeAIEtBBTwFmsUggABAgS6CSjgbhszL4FsAekJbCOggLdZpSAECBAg0ElAAXfallkJEMgWkH4rAQW81TqFIUCAAIEuAgq4y6bMSYAAgWyB7dIr4O1WKhABAgQIdBBQwB22ZEYCBAgQ2E7gUAFvl14gAgQIECBQJKCAi+BdS4AAAQLZAgr47f17kAABAgQIjBNQwOMsnUSAAAECBN4WUMBvU2U/KD0BAgQIjBVQwGM9nUaAAAECBN4SUMBvMXkoW0B6AgQIjBdQwONNnUiAAAECBF4KKOCXRB4gkC0gPQECcwQU8BxXpxIgQIAAgacCCvgpjy8JEMgWkJ7APAEFPM/WyQQIECBA4KGAAn5I4wsCBAhkC0g/V0ABz/V1OgECBAgQ+FFAAf/I4kMCBAgQyBaYn14Bzzd2AwECBAgQ+CaggL+R+IAAAQIECMwXWLmA56d3AwECBAgQKBJQwEXwriVAgACBbAEFvOr+zUWAAAECWwso4K3XKxwBAgQIrCrwJwAAAP//lVwoVAAAAAZJREFUAwDU5ALRcl29HAAAAABJRU5ErkJggg==10TIF B: First of all, we don't want Square, the sprite with nine clones to show the board, to move around. So I added another sprite, named Sprite. It's hidden, but can draw lines with its thick red pen. (Click on Sprite at the right to see its code.) The actual work is done in procedure DRAW WIN LINE. But instead of running DRAW WIN LINE in the Square sprite (this one), we TELL Sprite TO do it. 3.3.3.3: If the ninth move, the one that fills the board, causes a win, then the game isn't a tie even though no more moves are possible.3.3.3.5: There are many ways to do this. The way shown here uses a /flag variable/, i.e., a variable whose value is true or false. In this case, PLAYING is true if further moves are allowed.We modify makeBoard for TIF B because drawn lines are behind sprites on the stage, so the win line is hidden by the board. To fix that, we apply a ghost effect (transparency) to the board sprites. The value 30 for the ghost effect was found by experiment. Any more and the board is too faint; any less and the line is.3.3.3.TIF B starts here. The instruction below only needs to be run once. It makes a list of the two endpoints of each of the lines to mark a win. It must be in the same order as POSSIBLE WINNING TRIPLES. 3.3.3 TIF A This is quite complicated! We are asked to make a check, never mind details yet, after the eighth move, because that's when the last move is forced. But if the eighth move causes O to win (it has to be O because odd numbered moves are X and even numbered moves are O), then we shouldn't do this. That's why the IF around this code has to include a check of PLAYING. If O didn't just win, then we are going to imagine filling the final square with X (because move 9, an odd-numbered move, is always X). But we're not really going to change what's on the board, just what's in the BOARD list. (Really we shouldn't even do that; we should copy the list and change the copy. But if the eighth move has just happened and X can win on the next move, it's okay that we've already marked that square as belonging to X; we'll do it again when player X actually clicks the square.) It's just after the eighth move if there's exactly one number left in BOARD. We compute the list of numbers in BOARD, for two purposes: First we see if there's exactly one number. If so, we change that item of BOARD to X. Then, if X didn't win, we can announce a tie. Note: The code from 3.3.3.1 that checks for a tie on the ninth move is now never going to succeed, because we're catching ties early. But there's no need to remove it, just in case a player manages to click the ninth square before we locate it. Maybe mark it as obsolete in a comment. trueO,O,X,X,X,O,O,X,Xfalse-100,50100,50-100,0100,0-100,-50100,-50-50,100-50,-1000,1000,-10050,10050,-100-100,100100,-100-100,-100100,100