WEBVTT 00:00.610 --> 00:07.360 Sometimes you want a list of sordid elements haven't cared much so far about whether all our elements 00:07.360 --> 00:10.270 are sorted in some particular order. 00:10.270 --> 00:18.790 Sorting is also a very deep topic and there are many different algorithms you can use to do it but I 00:18.790 --> 00:23.850 want to briefly show you one way you can sort elements using a vector and the sort. 00:23.850 --> 00:27.420 Function of the Siebold plus standard library. 00:27.760 --> 00:38.040 First we need the actual sort function so to do that we just say include algorithm 00:40.950 --> 00:45.850 and before we actually sort it let's just go over what this does. 00:45.960 --> 00:53.550 Basically all we're doing is we're creating a vector of 20 elements initially and we're just giving 00:53.550 --> 00:55.410 it some random value. 00:55.620 --> 00:59.260 See we run it again. 01:03.780 --> 01:06.350 You read it again. 01:06.530 --> 01:12.540 You'll see that it has 20 just random values in a random order. 01:12.680 --> 01:17.710 And so there's no order to the list here. 01:17.710 --> 01:18.920 OK. 01:19.280 --> 01:26.350 So to actually sort everything we call the sort function. 01:26.420 --> 01:36.150 So call it by it's called sort and you just say it back dot gain 01:39.640 --> 01:43.240 it back dot and 01:47.710 --> 01:52.620 so you were using the begin and end functions of the vector. 01:52.720 --> 02:00.040 You can just think of these functions as a cursor to the first element in a cursor to the last element. 02:00.190 --> 02:08.570 We do the beginning and end here because we want to sort the entire vector so that does mean that sorc 02:08.610 --> 02:17.200 can actually do a partial sort of the vector if we wanted but we're not going to do that basically ever 02:17.200 --> 02:19.570 in discours. 02:19.900 --> 02:36.010 So we see here if we actually print out everything so say it's 0 x SPUs and we'll just output every 02:36.100 --> 02:36.890 out. 02:37.120 --> 02:41.880 So it ack. 02:42.130 --> 02:42.320 Or 02:46.450 --> 02:53.800 like that and it's also say this out sorted this 02:56.140 --> 03:03.830 initials so if you run this we should see it should be sorted. 03:03.950 --> 03:06.650 So here's the list. 03:06.650 --> 03:09.300 And here is a sort of list. 03:09.950 --> 03:18.520 And we see that it's in ascending order so things get bigger as you go down. 03:18.920 --> 03:25.350 What if we wanted to change how we wanted to sort this list. 03:25.400 --> 03:31.700 So say going in descending order instead of ascending or how would we do that. 03:31.880 --> 03:37.120 Well we do that by providing sort with a compare function. 03:37.130 --> 03:40.490 So in this case it's actually right out. 03:40.490 --> 03:47.970 So compare function will always return true or false and it will compare. 03:48.230 --> 03:50.140 So just say descending. 03:50.140 --> 03:50.820 Compare 03:54.690 --> 04:00.520 it will compare the two values. 04:00.700 --> 04:06.100 And this type that he that we're using here is the same type as the vector. 04:06.250 --> 04:11.540 So say x 1 and x 2. 04:11.890 --> 04:12.960 Just copy this 04:16.670 --> 04:26.310 piece down here and all this we'll do is we'll say x 1 turn x 1 greater than x 2. 04:30.840 --> 04:38.610 K so this function is for comparing whether the first argument should be before the second argument 04:38.670 --> 04:39.680 or not. 04:40.040 --> 04:44.020 OK so we'll use it here 04:48.310 --> 04:49.670 like this. 04:49.780 --> 04:52.920 And notice this is basically a function pointer. 04:52.930 --> 05:05.370 So the third parameter of this overloaded function sort will actually be a compare function. 05:05.380 --> 05:06.970 So if you run this 05:09.860 --> 05:18.710 see the rain last and we see that it will actually go in descending order and so descending because 05:19.430 --> 05:26.070 X1 should be before x 2 essentially k. 05:26.370 --> 05:31.590 So whatever you had before should be going that way if you want to be in ascending order again we could 05:31.590 --> 05:34.970 just put the sign in around it. 05:36.590 --> 05:40.750 And it's back into ascending order. 05:41.330 --> 05:44.490 This would change a little bit not too much. 05:44.510 --> 05:54.680 If we are using our own types say using a struct because how do you compare one struct type to another 05:54.680 --> 05:55.960 of the same type. 05:56.450 --> 06:05.810 This is less than or equal design doesn't work with our own created types and we will actually compare 06:07.190 --> 06:15.740 structure directly but we might compare say the individual members of the strikes but we'll look at 06:15.740 --> 06:18.620 how to do that in the next lecture.