WEBVTT 00:00.620 --> 00:08.990 We've seen a raise before which are contiguous size containers they contain whatever type that we send 00:08.990 --> 00:10.220 it to. 00:10.220 --> 00:16.430 We've also seen how to use or how to resize arrays by using dynamic memory. 00:16.450 --> 00:26.740 As we saw in the mini project well viscose plus standard has a type that can do all of all of this for 00:26.740 --> 00:29.140 us already built. 00:29.140 --> 00:31.720 So it's called a vector. 00:31.870 --> 00:36.400 And don't use the name vector with linear algebra vectors. 00:36.430 --> 00:38.310 These are completely different. 00:38.320 --> 00:43.780 This C++ vector is effectively a dynamic array. 00:43.780 --> 00:51.930 It will resize itself if you add more elements then had a capacity for the most interesting thing about 00:51.930 --> 00:56.730 vectors is that you can use them with any type. 00:56.730 --> 00:59.290 So how to use a vector. 00:59.320 --> 01:05.600 We have to say clewed vector. 01:05.630 --> 01:20.330 This day and if we wanted say a vector of integers we'd say vector in which this man gave it been. 01:20.570 --> 01:21.190 OK. 01:21.610 --> 01:23.980 So we have some new syntax here. 01:23.980 --> 01:28.750 These kind of angle brackets right here k. 01:29.450 --> 01:39.570 They're part of what is called templates and templates is a very very deep topic and far beyond the 01:39.570 --> 01:51.690 scope of this course but just know that if we want to make a vector in between these brackets here is 01:51.690 --> 01:55.080 the type that we want to hold in the vector k. 01:55.110 --> 02:02.410 So the entire thing this whole thing right here right here is the type. 02:02.710 --> 02:03.260 OK. 02:03.360 --> 02:05.940 So it's a vector of integers. 02:05.940 --> 02:13.540 In this case and this vector of integers we can actually add things to it. 02:13.620 --> 02:25.470 So if you wanted to add an integer at the back of the vector we could do this say it back and say push 02:25.470 --> 02:30.250 back five k. 02:30.910 --> 02:37.490 But say so this will actually add 5 to the end of the vector. 02:37.840 --> 02:38.420 OK. 02:38.670 --> 02:48.480 And I like to for my mental model of vectors it's really just the array and it's really just the array 02:48.480 --> 02:49.290 mental model. 02:49.350 --> 02:56.460 And same with strings arranged have the array mental models but with characters instead. 02:57.690 --> 03:03.390 And one nice thing is that you can get the size of the vector. 03:03.390 --> 03:26.680 So if I said see Ouch the size vector in that size x K This should give me one so the size of the vector 03:26.680 --> 03:27.010 you want. 03:27.010 --> 03:27.340 Right. 03:27.370 --> 03:35.620 So I have one element that I've added to the vector K and I could even get the capacity 03:38.500 --> 03:45.300 passively of the vector. 03:50.380 --> 03:55.750 So this is how many elements that are actually allocated in memory. 03:55.880 --> 04:08.770 Ok so if I say that it passive vector currently is one capacity your own if we wanted to have more capacity 04:10.760 --> 04:23.190 we could actually reserve it so we can actually say back Reserve and that's reserved 20 k. 04:23.580 --> 04:35.490 So the reserve will actually make the capacity of the vector at least big enough to contain an elements 04:35.580 --> 04:39.130 or in this case 20 it's OK. 04:39.600 --> 04:48.730 So if you're on this we see the capacity has changed to be 20 so there's 20 elements. 04:48.730 --> 04:49.360 OK. 04:49.530 --> 04:57.330 And you might ask OK what happens if I add more more elements then the capacity. 04:57.460 --> 04:57.950 OK. 04:58.170 --> 05:11.540 So I did that say this zero is less than say 20 in this case so they'll be 21 at the end. 05:11.540 --> 05:13.240 This say in at 05:17.740 --> 05:24.340 to push back. 05:24.620 --> 05:36.380 So you're right this so size is 21 and noticed that the capacity change so it changed to 40. 05:36.530 --> 05:41.690 And so it actually doubled the size of the capacity when we went over. 05:41.780 --> 05:53.230 In fact let me do this again and see it change at some point. 05:53.380 --> 05:53.810 OK. 05:53.810 --> 05:55.120 So let's just come at this. 05:55.120 --> 05:55.870 Ouch. 05:56.020 --> 06:03.820 So each time we add We'll check to see the size and to see if the capacity change through this 06:07.120 --> 06:08.630 clips do it. 06:09.020 --> 06:09.580 OK. 06:09.580 --> 06:21.030 So the size of the vector is to 20 20 20 20 20 20 k up until we add one more which then it doubled. 06:21.050 --> 06:21.290 Right. 06:21.310 --> 06:33.370 So once we added the twenty first element then the capacity changed K so it regrew the entire internal 06:33.370 --> 06:38.550 array that it uses to store all the integers. 06:39.150 --> 06:43.610 So that's that's really what a vector is at its heart. 06:43.630 --> 06:51.220 So it's dynamically changing array and then growing array. 06:51.520 --> 07:00.590 We can also say remove something from the vector say Interac. 07:01.060 --> 07:04.910 Pop back and doesn't take any arguments. 07:04.940 --> 07:11.400 And this will actually remove the last element 07:14.570 --> 07:15.440 in the vector 07:18.250 --> 07:23.780 so if we said we just comment this 07:27.340 --> 07:29.530 we should have 20. 07:29.650 --> 07:34.500 It's the sizes 20. 07:34.720 --> 07:40.850 And those of the capacity didn't change because it already knows that we can have more than that right. 07:40.870 --> 07:42.780 In our programs of our. 07:43.210 --> 07:45.590 And of course we can check. 07:45.700 --> 07:53.910 Well we could actually before we do that we could actually remove all the elements in the vector. 07:54.070 --> 07:56.910 So it's a Interac not clear. 07:59.010 --> 08:13.870 So this will remove all the elements in the vector gay and we can also check to see if the vector is 08:13.870 --> 08:14.730 empty. 08:18.000 --> 08:20.180 This or turn true if it's empty. 08:20.200 --> 08:21.650 So we say 08:24.600 --> 08:26.330 actor is empty 08:31.160 --> 08:32.070 else. 08:35.240 --> 08:42.350 Or. 08:42.390 --> 08:45.630 So this should only print that the is empty at the act. 08:45.710 --> 08:52.060 So it's an and after the clear we see that the vector is empty. 08:52.060 --> 08:53.770 So the size is zero. 08:53.780 --> 09:09.470 In this case and one last thing just like arrays we can actually set individual elements of the vector 09:09.890 --> 09:13.300 using this indexing operator. 09:13.430 --> 09:15.160 And just like arrays. 09:15.200 --> 09:18.820 So I say 0 is 5. 09:18.860 --> 09:21.960 Say and I can say See. 09:21.990 --> 09:23.190 Ouch. 09:23.320 --> 09:24.910 Ouch. 09:25.890 --> 09:28.580 0 is 09:33.420 --> 09:38.690 x. 09:39.120 --> 09:42.710 This. 09:42.900 --> 09:47.580 You see that act of 0 5. 09:47.860 --> 09:57.800 So you can access individual elements just like arrays. 09:57.860 --> 10:02.350 These will be the main functions we'll use in our projects. 10:02.630 --> 10:08.210 So I show you a few more that will be needing in our mini project. 10:08.210 --> 10:20.010 And if you want to see what else the vector type can do you can actually check out this link here. 10:24.020 --> 10:28.860 And you can see all the other functions that the vector has. 10:28.880 --> 10:37.010 Generally speaking vectors are far safer than using arrays and especially dynamically allocated trees 10:37.430 --> 10:45.890 and they're more convenient since since a lot of the work will be taken care of for you. 10:46.190 --> 10:49.170 For example resizing your array. 10:49.220 --> 10:53.390 One last thing is they're use with functions. 10:53.390 --> 11:02.970 So just like strings you want to pass a vector by reference k 11:10.080 --> 11:10.430 k. 11:10.440 --> 11:16.770 So if you want to add to it or change it in any way you should always be passing it by reference. 11:16.770 --> 11:24.850 Otherwise if you pass it by value it will do that kind of very expensive copy that we saw with strings. 11:24.910 --> 11:32.760 Or again if you want to not be able to change it you should pass it by constant reference so that's 11:32.820 --> 11:33.850 really yeah. 11:33.900 --> 11:42.690 And we'll be seeing some more examples of vectors and strings in the upcoming finale of The Mindy Project 11:43.140 --> 11:49.920 and and also in the game Space Invaders clone that we're right. 11:50.000 --> 11:56.410 And so I want to talk about sorting vectors in the next lecture.