WEBVTT 00:00.850 --> 00:09.580 Let's add a simple main function without parameters here and we're going to print provide a width. 00:10.330 --> 00:19.360 Basic input output using the include input output stream here and we're going to use the string in this 00:19.360 --> 00:22.060 practical practical example here. 00:22.060 --> 00:24.910 So include string here. 00:26.030 --> 00:37.270 So here above the main function, add a definition for the structure that represents a task in the list 00:37.280 --> 00:37.790 here. 00:38.870 --> 00:42.330 Task and task pointer here. 00:42.370 --> 00:46.670 P next and string description. 00:49.020 --> 00:49.350 Here. 00:50.370 --> 00:53.090 So this has two members. 00:53.100 --> 00:55.920 The guts of the object is the description. 00:56.880 --> 00:57.570 Item here. 00:57.570 --> 00:59.190 So in our example. 01:00.270 --> 01:07.260 Executing a task will involve the print printing, the description item to the console. 01:07.260 --> 01:14.100 So in an actual project, we most likely will have many items associated with the tasks and you may 01:14.100 --> 01:17.490 even have member functions to execute the task. 01:17.490 --> 01:26.010 But we have not covered the member functions in this course, which is the topic of another next lecture 01:26.010 --> 01:26.550 here. 01:26.550 --> 01:32.790 So the plumbing of the linked list is the other member P next here. 01:32.790 --> 01:40.560 So the task structure has not been completely defined at the point that the P next member is declared. 01:40.560 --> 01:45.060 So this is not a problem because the P next here is a pointer. 01:45.600 --> 01:53.970 So you cannot have a data member of any undefined or a partially defined type because the compiler will 01:53.970 --> 01:56.730 not know how much memory to allocate for it. 01:56.730 --> 02:03.130 So you can have a pointer member to a partial defined type because a pointer member is the same size 02:03.130 --> 02:06.430 irrespective of what it points to. 02:06.430 --> 02:12.190 So if we know the first link in the list, then we can access the whole list. 02:12.190 --> 02:16.510 And in our example this will be a global variable. 02:16.510 --> 02:19.570 So when constructing the list here. 02:20.540 --> 02:28.990 The construction functions need to know the end of the list so they can attach a new link to the list. 02:29.000 --> 02:30.470 Again, for convenience. 02:30.470 --> 02:37.640 We will make this global variable here and the following pointers after the definition here. 02:39.750 --> 02:40.110 Here. 02:41.250 --> 02:46.650 The following pointers after the definition of the task pointer like that. 02:46.650 --> 02:49.700 Here it and nullptr. 02:50.930 --> 02:53.840 VTR and task here. 02:57.530 --> 02:58.970 He current? 02:59.870 --> 03:01.080 No, Peter. 03:01.730 --> 03:06.500 So as it stands here, if we execute this. 03:07.280 --> 03:11.060 This code does nothing, but it's a good opportunity to compile the file. 03:11.090 --> 03:15.980 To test that, there are no errors in our code here. 03:16.100 --> 03:19.520 So let's add the task object to the list here. 03:19.520 --> 03:30.920 So in this project, the next thing to do is to provide the code, is to add, uh, add a new task to 03:30.920 --> 03:31.610 the task list. 03:31.610 --> 03:39.680 So this needs to create a new task object and initialize it appropriately and then add it to the list 03:39.680 --> 03:43.790 by adding the last link in the list to point to a new link. 03:43.790 --> 03:51.740 So above the main function here, add this new task here void queue. 03:53.270 --> 03:55.400 Task and const. 03:56.390 --> 03:58.070 Spring name. 04:00.380 --> 04:00.650 Here. 04:01.890 --> 04:11.160 So the parameter here is const this const the parameter is const because we will not change the parameter 04:11.160 --> 04:15.720 and we do not want to overheat of a copy being made. 04:15.990 --> 04:22.620 So by the way, I want to mention that this is not the not just a const variable, this is const reference. 04:22.620 --> 04:29.310 As you know, we make this ampersand before the variables to make them references. 04:29.310 --> 04:37.380 So the first thing in this function, the function this function must do is create a new link. 04:37.380 --> 04:44.010 So we're going to add the task pointer task P task. 04:45.070 --> 04:47.050 Task T task. 04:48.730 --> 04:49.180 Here. 04:49.840 --> 04:50.800 New task. 04:53.170 --> 04:55.090 And task. 04:56.010 --> 04:57.090 This operator. 04:57.090 --> 04:59.700 You know it from the previous lectures. 05:00.600 --> 05:02.880 Description and name. 05:05.010 --> 05:06.330 P task. 05:07.200 --> 05:11.250 P next year and we can assign it to nullptr. 05:11.550 --> 05:19.680 So the first line creates a new link on the free store and following lines to initialize it. 05:19.680 --> 05:24.000 So this is not necessarily the best way of initializing such an object. 05:24.000 --> 05:31.410 And a better mechanism is a constructor, so the constructors will be covered in next lectures here. 05:31.410 --> 05:37.700 So notice that the P next year P next item is initialized to nullptr. 05:37.710 --> 05:42.420 So this indicates that the link will be at the end of the list. 05:42.420 --> 05:46.950 So the final part of this function adds the link to the list. 05:46.950 --> 05:50.520 So this is it makes the link the last in the list. 05:50.520 --> 05:57.900 So however, if the list is empty, it means that the this link is also the first link in the list. 05:57.900 --> 06:03.360 So the code must perform both actions here and we're going to add. 06:04.820 --> 06:05.570 Here. 06:09.350 --> 06:10.220 If. 06:12.460 --> 06:12.910 Here. 06:17.920 --> 06:18.760 If. 06:19.030 --> 06:20.640 Nullptr. 06:21.890 --> 06:22.760 He had. 06:24.540 --> 06:27.060 Then he had. 06:28.110 --> 06:29.010 He task. 06:30.680 --> 06:31.820 He task. 06:33.970 --> 06:34.270 Oops. 06:38.610 --> 06:39.090 Okay. 06:42.880 --> 06:49.570 T hat is p task and then p current. 06:50.310 --> 06:51.210 He test? 06:53.600 --> 06:54.350 Else. 06:56.700 --> 06:59.700 Here the current. 07:02.500 --> 07:06.640 He next and it equals to p task. 07:08.190 --> 07:09.360 The current. 07:11.920 --> 07:13.780 The task here. 07:13.780 --> 07:20.250 So the first line of the code checks to see if the list is empty. 07:20.260 --> 07:28.270 So if the if the P hit is null, this it means that the there are no other links. 07:28.840 --> 07:31.990 And so the current link is the first link. 07:31.990 --> 07:39.550 So and so both P hit and the P current are initialized to the new link pointer. 07:39.550 --> 07:44.230 So if there are existing links in the string, the links has to be added to the last link. 07:44.230 --> 07:53.710 So in the s class here, the first line, the first line makes the last link point to the new link and 07:53.710 --> 07:54.850 the second line. 07:54.850 --> 07:58.810 Initialize the p current with the new link pointer. 07:58.810 --> 08:06.760 Making the new link to the last link for any new insertions to the list so the items are added to the 08:06.760 --> 08:11.720 list by calling this in the main function. 08:11.720 --> 08:16.160 So in this example we will queue the tasks to a wallpaper room. 08:16.160 --> 08:23.570 So this involves removing the old wallpaper, filling any holes in the wall, sizing the wall and then 08:23.600 --> 08:25.850 hanging the passage wallpapers to the wall. 08:25.850 --> 08:31.760 So you have to do these tasks in this order so you cannot change the order. 08:31.940 --> 08:36.050 So these tasks are ideal for a link list. 08:36.050 --> 08:39.890 So in the main function we're going to use a queue task here. 08:40.490 --> 08:44.930 As you know, we made this void function in this here. 08:45.740 --> 08:54.560 We're going to use the queue task and remove old wallpaper for example, and then we're going to use 08:54.560 --> 08:55.340 it again. 08:55.610 --> 08:57.500 Fill holes. 08:59.010 --> 09:02.330 Here and size walls. 09:03.700 --> 09:10.270 And to task the hang new hang new wallpapers. 09:11.230 --> 09:16.270 So after the last line, the list has been created. 09:17.150 --> 09:23.570 So the heat variable points to the first item in the list and you can access any other item in the list 09:23.570 --> 09:29.930 simply by following the next member from one list to the next so you can compile the code. 09:29.930 --> 09:32.600 But there is no output as you see here. 09:32.630 --> 09:39.500 Worse, as the code center is a memory leak, so the program has no code to delete the memory occupied 09:39.500 --> 09:40.910 by the task object. 09:40.910 --> 09:45.110 So on the free store by the new operator here. 09:45.110 --> 09:53.390 So in next lecture we're going to create that delete the task list command in C plus plus. 09:53.390 --> 09:55.670 So I'm waiting you in next lecture.