WEBVTT 00:00.750 --> 00:05.120 I said earlier that are pointers and arrays almost work interchangeably. 00:05.380 --> 00:13.320 Well that only applies to one dimensional or it is with pointers pointers with multi-dimensional arrays 00:13.370 --> 00:17.430 is a little bit different than using pointers with one dimensional right. 00:17.760 --> 00:33.720 So say we had this array A to the Marybel last time you this well you'd think you could do something 00:33.720 --> 00:40.810 with this. 00:41.150 --> 00:43.250 And unfortunately you can't. 00:43.250 --> 00:47.750 So you think you could do this because there's you know one dimension here in one dimension and there 00:47.750 --> 00:55.160 and maybe you know if you had one pointer and another pointer kind of in between here that would kind 00:55.160 --> 00:58.720 of compensates for this one dimension the other dimension. 00:59.000 --> 01:02.280 Well unfortunately this doesn't work right. 01:02.330 --> 01:08.610 So an error you can't initialize that variable with the array. 01:08.760 --> 01:15.000 So it's saying so how would we have a pointer to a 2D array. 01:15.030 --> 01:18.240 Well we could do this instead. 01:20.340 --> 01:21.160 When juror 01:24.860 --> 01:32.820 this and have B 10 here is there this needs to be the same way. 01:33.730 --> 01:37.690 And you could just do that k. 01:37.710 --> 01:43.900 So what this is is a pointer to an array of 10 items. 01:44.490 --> 01:46.970 It does exactly what you want. 01:46.980 --> 01:51.360 So let's see an example for example. 01:51.420 --> 01:54.410 So let's say we had constant max. 01:54.500 --> 01:55.960 Call it 10 here. 01:59.210 --> 02:00.170 Max 02:04.110 --> 02:04.740 it's like that 02:07.390 --> 02:15.280 and sleep over all the rows. 02:17.930 --> 02:20.600 In all columns 02:28.090 --> 02:33.730 in just say pointer are in. 02:34.040 --> 02:40.590 King can do this because again sort of work like arrays at least in this dimension. 02:40.590 --> 02:41.410 Right. 02:42.000 --> 02:45.330 And of course we have an array of them so we can use. 02:45.330 --> 02:46.890 See here. 02:47.370 --> 02:56.730 This doesn't matter too much or it's a sign and some values and just output those values are and who 02:56.730 --> 02:59.680 are. 03:01.640 --> 03:02.660 C. 03:02.850 --> 03:04.500 Good to see 03:09.620 --> 03:20.620 you pointer of R and C. 03:20.770 --> 03:25.430 So if you're in this should see actually work. 03:25.480 --> 03:32.730 So are using that pointer to modify the to the array. 03:32.730 --> 03:33.000 Right. 03:33.070 --> 03:42.500 So you go through the first row and then we just give its values and the second Aronne its values right. 03:42.970 --> 03:50.780 And so on and so you can do this as well. 03:50.850 --> 03:51.910 Dynamic memory. 03:51.930 --> 03:54.260 And in fact in a couple of different ways. 03:54.280 --> 04:10.040 So the first way I'll show you is say we don't need this anymore and we can say this new and in Max 04:11.510 --> 04:14.780 and x a. 04:14.830 --> 04:22.660 So this will actually create a contiguous to the array in memory and has pointer point to it. 04:23.200 --> 04:31.630 And just like normal we can do is delete this pointer. 04:31.880 --> 04:38.660 So this is exactly the same and it works at the same see the same result. 04:41.620 --> 04:49.710 Well let me show you one more way you could create a two tier and then is using an int pointer pointer 04:49.710 --> 04:51.750 that I showed before. 04:52.040 --> 04:58.720 And so now you're going to see why we couldn't do the end pointer pointer before. 04:58.940 --> 05:08.100 So it's a pointer this and watch say new 05:11.530 --> 05:22.310 winter or re k so this creates a new pointer and you're wondering like what kind of direction that R8 05:22.310 --> 05:23.040 goes. 05:23.050 --> 05:27.460 Well in this case you can kind of think of it as it goes sort of down. 05:27.530 --> 05:33.110 So it's kind of this first column but it's the first column of pointer's. 05:33.220 --> 05:36.880 So it's an array of pointers. 05:36.900 --> 05:54.790 So then how we set all the arrays on it is this the loop or are equals zero AR's less than max are A-plus 05:54.830 --> 05:57.050 plus. 05:57.580 --> 06:08.540 And the pointer of our equals new int max. 06:08.850 --> 06:18.560 So each of these pointers now will be assigned an array of this Max like 06:21.530 --> 06:28.670 so now you can use it just like you did for an. 06:28.720 --> 06:31.870 So you can 06:48.180 --> 06:49.180 we help 06:53.010 --> 06:55.540 can see in kind of use of like before 06:58.040 --> 07:02.100 and but we haven't cleaned it up yet. 07:02.180 --> 07:02.840 OK. 07:03.230 --> 07:05.360 So notice that we had 07:08.000 --> 07:17.640 so that we made kind of the sort of big column of integer pointer or like that array of integer pointers. 07:17.960 --> 07:19.160 This line here. 07:19.370 --> 07:23.090 And then we kind of made all the arrays after for each row. 07:23.420 --> 07:29.170 Well we have to do that in reverse if you want to clean it up so we have to clean up all the rows first. 07:31.160 --> 07:32.080 Yes. 07:35.880 --> 07:40.610 So those leaks are 07:42.920 --> 07:47.410 or and then we delete 07:50.120 --> 08:02.200 the pointer K so that it does everything in reverse deletes all the rows first but we made all the rows 08:02.200 --> 08:03.180 second. 08:04.000 --> 08:08.780 And they made this pointer first and then we have to delete the pointer last. 08:09.050 --> 08:12.600 So it kind of goes in reverse order to its creation. 08:13.670 --> 08:18.900 So what is the difference between the two. 08:19.120 --> 08:23.950 Well this what we have for ain't 08:26.980 --> 08:28.810 for Star pointer. 08:31.560 --> 08:37.140 Like that's new in x. 08:37.200 --> 08:41.280 Max Right. 08:41.320 --> 08:44.710 This one is contiguous in memory. 08:44.770 --> 08:45.320 Right. 08:45.430 --> 08:49.330 So in memory they actually are all next to each other. 08:50.320 --> 08:59.800 Unlike this one which is possibly piecemeal in terms of the memory out because we don't know what addresses 09:00.160 --> 09:03.520 the new operator will return to us. 09:03.520 --> 09:06.040 They might be contiguous but maybe they're not. 09:06.100 --> 09:07.590 So we don't know. 09:07.870 --> 09:09.520 And when you use them. 09:09.520 --> 09:17.650 Well if you want something pretty flexible in terms of the row and column sizes you should use the second 09:17.650 --> 09:23.120 one this in your pointer method for that case. 09:23.200 --> 09:29.110 But if you know the size or you can sort of calculate the size somehow then you should probably just 09:29.110 --> 09:33.380 use this sort of contiguous one because this is usually more efficient. 09:33.590 --> 09:34.660 OK. 09:35.170 --> 09:44.740 So we'll talk more about pointer pointer and just pointers to pointers more in the next lecture.