WEBVTT 00:00.090 --> 00:07.050 Hello again! In this video, we are going to have a practical on Conway's Game of Life. Before we get started, 00:07.050 --> 00:09.630 there are a couple of things we need to think about. 00:09.960 --> 00:14.340 The first one is that C++ does not, in fact, have a standard graphics library. 00:15.090 --> 00:19.830 There was talk of adding one in C++20, but unfortunately that did not happen. 00:20.880 --> 00:28.560 We could use a third-party graphics library, but that is a bit of a support headache! So I would prefer to 00:28.560 --> 00:30.120 save that for later in the course. 00:30.780 --> 00:33.840 So we're going to implement this solution in text mode. 00:35.070 --> 00:40.920 The other issue is that a cellular automaton requires an infinite grid, and obviously our computer 00:40.920 --> 00:42.960 only has a finite amount of memory. 00:43.470 --> 00:46.170 So we need somehow to restrict the size of the grid. 00:46.920 --> 00:52.800 What we are going to do is, we are going put a border of cells around the actual simulation, and the cells 00:52.800 --> 00:55.920 in that border are going to be permanently unpopulated. 00:56.370 --> 01:02.040 So even if the rules of Life say that one of these border cells should become populated, we are going 01:02.040 --> 01:04.080 to ignore that, and leave it empty. 01:04.650 --> 01:10.530 So this means that the cells are going to be restrained within that border, and they cannot move outside 01:10.530 --> 01:12.170 the border of our simulation. 01:15.070 --> 01:19.990 We are going to use a two dimensional array to represent the grid. Hence the last video! 01:20.770 --> 01:21.460 The elements 01:21.460 --> 01:25.210 of this array are going to be a class which represents a cell on the grid. 01:26.320 --> 01:34.390 The game is going to be played inside a standard 80x24 terminal, in text mode, and we are going to use 01:34.390 --> 01:39.370 so-called "ANSI escape codes" for displaying these cells on the terminal. 01:42.440 --> 01:46.550 In the days before everyone had a computer on their desk at work, 01:46.820 --> 01:49.190 people used to have so-called "dumb terminals". 01:49.640 --> 01:53.330 This was something that looked like a keyboard, and something that looked like a television screen. 01:53.810 --> 01:55.520 So you type something in on the keyboard. 01:55.850 --> 02:00.260 It would go to a central computer and the central computer would send something back, which was displayed 02:00.260 --> 02:00.920 on the terminal. 02:02.120 --> 02:05.930 And there are various commands for changing the way that the output appears. 02:06.350 --> 02:11.810 There is actually a standard, made by ANSI: the American National Standards Institute, I think. 02:12.290 --> 02:16.010 And these can be used by programs, to change the way that output is displayed. 02:16.550 --> 02:20.870 So you can use different coloured text, you can make the text bold or italic, and so on. 02:21.620 --> 02:26.780 And what we are interested in here is, you can make text appear at certain positions on the screen. 02:29.300 --> 02:34.490 These ANSI codes all begin with the escape character. So that that corresponds to pressing the escape key on 02:34.490 --> 02:35.090 your keyboard. 02:35.600 --> 02:37.460 You do not actually enter these codes yourself. 02:37.460 --> 02:39.860 They are something that the program sends to the terminal. 02:40.700 --> 02:46.700 So we have the escape character, followed by a square bracket. And 1b is the hexadecimal code for 02:46.700 --> 02:47.210 "escape", 02:47.720 --> 02:55.460 in the ASCII character set. The commands we are going to use are to move the cursor to a given row, and 02:55.460 --> 02:58.790 a given column within that row, and then display a character. 02:59.480 --> 03:05.210 To do that, you have the escape character, then the square bracket, then the row number, semi-colon, column 03:05.270 --> 03:09.470 number and capital H. And it has to be a capital, not lower-case. 03:10.370 --> 03:13.730 The other one is to clear the screen and return the cursor to the "home" position. 03:14.030 --> 03:16.070 So that means the top left of the screen. 03:16.730 --> 03:20.210 And that is the escape character, square bracket, two, capital J. 03:24.670 --> 03:31.030 Nowadays we have computers with graphical windowing environments, and they have consoles which can emulate 03:31.120 --> 03:33.670 one of these "ANSI-compatible" terminals. 03:34.810 --> 03:39.400 When I first thought up this exercise, I thought it would be nice and simple, but it is actually not quite 03:39.400 --> 03:40.720 as simple as I hoped for. 03:41.440 --> 03:47.410 If you have something which is descended from Unix, so that includes OSX and Linux, then the terminal 03:47.410 --> 03:49.720 should normally support this automatically. 03:50.650 --> 03:56.170 If you're perhaps running in full-screen text mode, or using single-user mode, if your terminal does 03:56.170 --> 03:59.410 not support these, then there is an environment variable "TERM". 03:59.650 --> 04:00.880 And you can set that to 04:00.880 --> 04:05.140 some value, which represents terminal which does support ANSI commands. 04:07.990 --> 04:08.920 For Windows, 04:08.920 --> 04:15.220 it is a bit more complicated. If you are using MinGW or Cygwin for your C++ compiler environment. 04:15.850 --> 04:19.390 These emulate a UNIX environment, so they support ANSI commands. 04:21.570 --> 04:28.350 If you're using PowerShell 5.1 or later to run your program, or Windows Terminal. Which is not the default 04:28.350 --> 04:30.270 command line, that's a separate program. 04:31.050 --> 04:36.300 If you have one of those, then that will support the command codes. There are also some third-party 04:36.300 --> 04:42.450 terminal programs you can install. If you are using the default command line in Windows, which is the 04:42.450 --> 04:44.490 one that pops up when you run Visual Studio. 04:45.180 --> 04:51.370 This does support ANSI commands, if you are using Windows 10, and if you put in some extra code to 04:51.370 --> 04:51.900 enable it. 04:53.070 --> 04:54.780 So - I will give you the code 04:54.780 --> 04:55.200 to do that. 04:58.440 --> 05:03.660 So the actual logic of the program itself. We are going to have two grids: one which will represent 05:03.660 --> 05:08.280 the current generation, and one which will represent the next generation. 05:08.910 --> 05:14.970 And then we are going to calculate if the cells in the current generation will survive or be populated 05:14.970 --> 05:15.960 in the next generation. 05:17.100 --> 05:21.390 So we start off by creating a grid object, to represent the initial generation. 05:22.290 --> 05:26.250 We populate the cells in that initial grid at random. Then we display it. 05:27.840 --> 05:32.190 Then we create a second grid object, which will represent the next generation. 05:33.630 --> 05:38.340 And then we go through, and calculate which cells will survive from this generation to the next generation, 05:38.700 --> 05:40.830 and which ones are going to be newly populated. 05:41.400 --> 05:43.620 And then we populate the next generation grid. 05:44.520 --> 05:47.280 Then we copy this grid over the current generation grid. 05:47.880 --> 05:55.110 So, what was the next generation now becomes the current generation, and the first generation is superseded. 05:55.860 --> 05:59.510 And then we display the new values of the current generation grid. 06:00.060 --> 06:00.720 And then we go back. 06:00.720 --> 06:02.550 We create another grid for the next generation. 06:02.580 --> 06:05.160 We calculate what cells will be in that next generation. 06:05.700 --> 06:09.240 Then we copy over the current generation, display the current generation, and so on. 06:09.510 --> 06:10.920 So it is really all one big loop.