WEBVTT 00:01.080 --> 00:01.890 In this video, 00:01.890 --> 00:04.920 we are going to continue implementing Conway's Game of Life. 00:05.700 --> 00:07.710 We are going to look at the source code in this video. 00:08.130 --> 00:12.510 I thought it would only need one or two videos, but in fact, it has needed four. 00:12.570 --> 00:14.490 So, apologies for that. 00:16.590 --> 00:19.290 Let's start off by looking at live.h. 00:19.680 --> 00:22.470 This has all the parameters for the simulation. 00:23.370 --> 00:29.670 The characters for cell will be capital X, if the cell is alive, and a space if the cell is empty. 00:29.940 --> 00:31.080 Which seems appropriate. 00:32.430 --> 00:36.000 We are going to be displaying this on a standard ANSI compliant console. 00:36.630 --> 00:42.450 This has rows, which go from 1 to 24, and columns, which go from 1 to 80. 00:43.390 --> 00:45.970 We are also going to have a border of 00:47.080 --> 00:49.540 cells which are permanently unpopulated, around this. 00:49.600 --> 00:55.050 So that will correspond to row 0, column 0, row 24 and column 80. 00:55.510 --> 01:01.810 So the maximum possible row number for a cell that is going to be displayed will be 23, and the maximum 01:01.900 --> 01:03.970 possible column number will be 79. 01:05.080 --> 01:06.280 Then we have the parameters 01:06.280 --> 01:08.980 that Conway came up with. A live cell 01:08.980 --> 01:15.910 needs two or three neighbours to survive, and an empty cell needs exactly three live neighbours to become 01:15.910 --> 01:16.570 populated. 01:19.370 --> 01:20.720 In the main() function, 01:20.720 --> 01:24.200 we start off by telling the user what to expect, and what to do. 01:24.950 --> 01:27.020 Then we wait for them to press the return key. 01:27.740 --> 01:30.110 This is just the standard input. 01:30.560 --> 01:33.320 It will stop and wait until the user presses the return key. 01:33.650 --> 01:36.530 If they enter any other characters, then that will just be ignored. 01:37.560 --> 01:39.080 I will come back to this bit in a minute! 01:41.370 --> 01:46.830 Then we create a grid object, which will contain the first generation of cells. 01:47.790 --> 01:50.010 We populate these cells at random. 01:51.580 --> 01:53.860 And then we display this initial generation. 01:55.000 --> 01:59.440 Then we wait for the user to press the return key, when they are ready to go on to the next iteration. 02:00.850 --> 02:06.520 Then we create this object, which we use for calculating which cells will be populated in the next generation. 02:07.300 --> 02:12.070 And then we copy all the cells, from the next generation over our current generation. 02:12.610 --> 02:14.650 So we started off with the first generation. 02:15.040 --> 02:17.830 Then we calculated which cells are alive in the second generation. 02:18.430 --> 02:21.340 And then we copied all the cells over the current generation. 02:21.760 --> 02:25.450 So the current generation now has the second generation of cells. 02:26.110 --> 02:27.520 Then we go back to the start of the loop. 02:27.970 --> 02:28.720 We display it. 02:29.410 --> 02:30.100 Gets input. 02:30.520 --> 02:32.260 Calculate the third generation. 02:32.920 --> 02:33.590 Display that. 02:33.610 --> 02:34.940 And keep going on and on. 02:34.960 --> 02:35.500 And so on. 02:37.890 --> 02:41.550 The cell class is really just a wrapper around a Boolean. 02:42.300 --> 02:46.020 This will be true if the cell is alive, and false if it is empty. 02:46.920 --> 02:50.070 We have a constructor which sets the status to false. 02:50.430 --> 02:52.530 So by default, all the cells will be empty. 02:54.210 --> 03:00.480 We can draw a cell at a particular position on the grid. And then we have some getter and setter functions. 03:01.170 --> 03:04.500 So we can set the boolean to true, to make the cell alive. 03:05.160 --> 03:07.290 We can set it to false, to make it empty. 03:07.890 --> 03:10.530 And we can find out whether the cell is alive. 03:14.120 --> 03:20.120 To draw the cell, we use one of these ANSI escape commands, the one which will move the cursor 03:20.120 --> 03:21.050 to a given position. 03:21.890 --> 03:24.150 These commands were designed by engineers, 03:24.200 --> 03:25.250 so they start from one. 03:25.720 --> 03:29.300 Unlike computer scientists, which have our array starting from zero. 03:29.990 --> 03:34.370 So we need to add 1, to get the character displayed in the correct place. 03:35.690 --> 03:40.820 So we send this escape code to the screen, which will move the cursor to the correct position, and 03:40.820 --> 03:44.060 then we send the character that we want to display at that position. 03:47.270 --> 03:50.450 The grid has an array of these cells. 03:51.440 --> 03:55.760 We need to add 2 to the dimensions, to allow for the borders. 03:57.530 --> 04:00.620 We can create a cell at a given position. 04:00.630 --> 04:01.790 We can make it alive. 04:02.630 --> 04:04.010 We can draw all the cells. 04:04.820 --> 04:07.100 We can populate the cells at random. 04:08.360 --> 04:12.650 And we have some functions for calculating what happens in the next generation. 04:13.220 --> 04:15.460 This non-member function controls the process. 04:15.470 --> 04:17.870 It takes the old generation and the new generation. 04:18.620 --> 04:24.380 We have a member function which will determine whether a live cell will survive to the next generation, 04:24.890 --> 04:30.290 a member function which determines whether an empty cell will become populated, and then a member function 04:30.290 --> 04:35.300 which will update this grid object, with the data from the next generation. 04:39.660 --> 04:43.260 The create() function just calls the create() function for the cell 04:43.260 --> 04:44.190 in that position. 04:44.490 --> 04:46.580 So this will make that cell to come to live. 04:47.820 --> 04:50.760 If we are drawing all the cells, we need to clear the screen first. 04:50.940 --> 04:53.550 So we send the ANSI escape command for that. 04:54.540 --> 04:56.580 Then we iterate over all the grid's - 04:57.510 --> 05:00.420 then we iterate over all the cells, including the ones in the border. 05:00.840 --> 05:03.240 And then we draw each cell in the right place. 05:06.160 --> 05:08.140 For populating the cells at random, 05:08.440 --> 05:15.730 we iterate over all the cells in the visible grid, and then we do this calculation. And this will populate 05:16.000 --> 05:16.900 the cell. 05:17.710 --> 05:23.580 A factor of 5 means there is a one in 5 probability, so at 20% of the cells will be populated and 05:23.600 --> 05:24.910 80% will be empty. 05:25.810 --> 05:30.160 If we change this to 10, for example, then that will be a one in 10 probability. 05:30.400 --> 05:32.650 So the initial grid would be much emptier. 05:34.330 --> 05:39.580 I am not going to seed the random number generator here, because I want to get the same output every 05:39.580 --> 05:42.840 time. Because I want to test and demonstrate. 05:42.850 --> 05:44.620 And for that you need consistent output. 05:45.430 --> 05:50.470 Obviously, if you were doing this for real, you would uncomment this and seed the random number generator, 05:50.920 --> 05:52.990 so you would get different output every time you run it. 05:55.720 --> 06:01.240 Then we have this function for determining whether a live cell will survive to the next generation. 06:02.140 --> 06:04.240 First, we check that there is a live cell there. 06:04.510 --> 06:06.370 If the cell is empty, there is nothing to survive. 06:06.370 --> 06:07.540 So we return false. 06:09.380 --> 06:15.050 Then we go through the neighbours of this cell. We call the is_alive() member function and add up the 06:15.050 --> 06:15.550 results. 06:16.100 --> 06:19.260 And that will give us the number of live neighbours for that cell. 06:20.390 --> 06:24.440 If we have too many or too few, then the cell will not survive and we return false. 06:25.220 --> 06:30.320 And if we survive to the end of the function, then the cell will survive to the next generation. 06:32.950 --> 06:35.680 Then we have a very similar function for empty cells. 06:36.190 --> 06:38.410 If there is a live cell, we return false. 06:39.130 --> 06:41.230 We find the number of live neighbours. 06:41.920 --> 06:44.410 And if we have the right number, we return true. 06:44.410 --> 06:45.340 Otherwise false. 06:48.430 --> 06:49.540 The update() function 06:49.540 --> 06:55.330 just goes through all the visible cells in the grid, and it copies the value of the cell, from the 06:55.330 --> 06:57.910 new generation, into the current generation. 07:00.960 --> 07:04.380 And then we have this function, which oversees the calculation process. 07:04.560 --> 07:07.170 It takes the old generation and the new generation. 07:07.860 --> 07:14.250 It iterates over every cell in the grid, and then it determines whether the cell in the current grid 07:14.250 --> 07:14.940 will survive. 07:15.360 --> 07:17.370 And if so, it creates this in the new grid. 07:17.790 --> 07:19.860 And similarly for empty cells. 07:23.460 --> 07:27.840 Going back to the main function, there is some code which you need to uncomment, if you are using Visual 07:27.840 --> 07:31.680 Studio or anything else that runs in Windows Console. 07:32.580 --> 07:34.500 I will show you what happens first if you do not do that. 07:38.140 --> 07:38.710 So there we are. 07:38.890 --> 07:39.950 "Conway's Game of live." 07:39.970 --> 07:42.580 "Press the return key to display each generation". 07:43.870 --> 07:45.130 And then we get all this gibberish! 07:45.940 --> 07:49.450 So the Windows Console has received all these ANSI escape commands. 07:49.930 --> 07:53.290 But it does not know what to do with them, so it just displays them, without interpreting them. 07:57.010 --> 07:59.260 So I needs to include this ansi_escapes.h, 07:59.620 --> 08:01.750 which is this file. 08:02.200 --> 08:07.960 So this declares two functions, which will put the console into a state where it processes ANSI commands. 08:08.560 --> 08:11.320 And then, at the end, it will put it back to how it was initially. 08:12.280 --> 08:15.010 And I think I found this code on Microsoft's website. 08:15.250 --> 08:17.800 It is all low level Windows stuff. 08:18.610 --> 08:22.480 All the code for this simulation is available as a downloadable resource. 08:23.110 --> 08:27.370 So you can you compile yourself, look through it, and see for yourself how it works. 08:27.910 --> 08:30.280 I am not a Windows expert, so I am not going to go into this. 08:32.760 --> 08:34.740 So I need to include this file. 08:35.190 --> 08:38.970 I also need to set up the console, before we display any output. 08:40.720 --> 08:44.170 And then at the end, I need to put things back, how I found them. 08:45.820 --> 08:46.810 So let's try this again. 08:48.310 --> 08:49.120 Ah yes, that is much better. 08:49.930 --> 08:52.660 So if we look at this, we have the border around the cells. 08:52.660 --> 08:53.410 It is rather thin. 08:54.640 --> 08:58.150 Then we have a cell at row 1, column 1. 08:58.720 --> 09:00.760 This has just one live neighbour. 09:02.170 --> 09:04.570 This cell here has three live neighbours. 09:05.410 --> 09:07.030 This has one live neighbour. 09:08.080 --> 09:09.820 This has three live neighbours. 09:10.720 --> 09:14.140 And this has only two live neighbours. That one there is actually empty. 09:14.800 --> 09:18.580 So in the next generation, we expect these two will have disappeared. 09:18.610 --> 09:23.140 We have a cell there, and then two cells there. And nothing down here. 09:25.540 --> 09:26.110 And there we are. 09:27.070 --> 09:30.250 And then we keep on pressing return, to get through the generations. 09:35.230 --> 09:38.200 And you can see structures starting to appear like this one. 09:38.200 --> 09:39.790 So there are some stable structures. 09:40.300 --> 09:45.760 For example, if you have a ring, every cell in the ring has exactly two live neighbours. 09:46.150 --> 09:47.680 So these will keep each other alive. 09:48.130 --> 09:53.350 So a structure like this could survive for generations, unless some other structure comes along and 09:53.590 --> 09:54.310 disrupts it. 09:58.380 --> 09:59.730 So, like that. 09:59.730 --> 10:02.880 So you see, the ring has now been merged into a bigger structure. 10:06.000 --> 10:07.320 And then we have another one down here. 10:07.320 --> 10:09.090 This is another stable structure. 10:12.460 --> 10:14.290 So what can you do to improve this? 10:15.190 --> 10:19.330 Well, for example, you might want to leave this running for a long time to see what happens. 10:19.330 --> 10:24.880 And having to sit there and keep pressing the return key might get a bit tedious. So you could just run it 10:25.630 --> 10:28.300 in a flat-out loop, or you could put a sleep in, or a pause. 10:28.930 --> 10:33.430 And the way to do that will depend on your operating system, so you can look that up. 10:34.000 --> 10:38.920 Or alternatively, there is a way to do that in C++11, which I will cover later. So you can try that 10:38.920 --> 10:40.090 out for yourselves if you like. 10:41.110 --> 10:46.780 Another thing is, it is quite hard to keep track of which cells are appearing and disappearing between 10:46.780 --> 10:47.440 iterations. 10:48.280 --> 10:53.800 So you could have another grid, which you display in between the current generation and the next generation. 10:54.820 --> 11:00.940 And on this in-between grid, you have the cells which are dying in red, maybe. The cells which are 11:00.940 --> 11:04.360 being born in green, and the cells which survive in blue. 11:06.220 --> 11:11.260 I have chosen a solution which is easy to implement, but it is not very efficient or accurate. 11:11.800 --> 11:17.860 We have this border of empty cells around it, which stops cells wandering off the edge of the simulation. 11:17.860 --> 11:19.240 But that is not actually correct. 11:19.870 --> 11:25.450 If you look at the Wikipedia page for Conway's Game of Life, there are some ideas about how to make 11:25.450 --> 11:29.800 this more extensible, without using too much memory or CPU time. 11:30.520 --> 11:34.660 And there are also some variants on the Game of Life, variants on the Conway rules, and you could 11:34.660 --> 11:35.500 look at those as well. 11:36.730 --> 11:41.590 And of course, if you are into graphics or GUI programming, you can make this look a lot flashier. 11:42.610 --> 11:44.120 Okay, so that is it for now. 11:44.140 --> 11:45.700 I am doing control-C to escape! 11:46.300 --> 11:47.200 I will see you next time. 11:47.200 --> 11:49.320 But until then, keep coding!