WEBVTT 00:00:01.040 --> 00:00:04.380 If only the first dimension is dynamic and the rest of them can 00:00:04.380 --> 00:00:07.740 be static, there is a better way to create a multidimensional 00:00:07.740 --> 00:00:11.980 array on the heap with the good, old two‑square‑bracket syntax. 00:00:11.980 --> 00:00:14.060 But before I show you, 00:00:14.060 --> 00:00:18.250 I want to first clarify the difference between specific types of pointers. 00:00:18.640 --> 00:00:23.330 This is a pointer to an integer which points to the first of 4 bytes 00:00:23.330 --> 00:00:27.620 which make an integer, so when we dereference this pointer we will 00:00:27.620 --> 00:00:31.570 get an integer, and the pointer arithmetic of this pointer will work 00:00:31.580 --> 00:00:33.960 in the increments of 4 bytes. 00:00:34.740 --> 00:00:39.550 And now, what if I had an array of integers and I pointed this pointer 00:00:39.550 --> 00:00:43.130 to this array? This is still a pointer to an integer. 00:00:43.140 --> 00:00:46.490 It points to the first integer from this array. 00:00:46.500 --> 00:00:50.220 It has no idea that this is an array, but we can still use it as an 00:00:50.220 --> 00:00:52.850 array name because of the pointer arithmetic. 00:00:54.040 --> 00:00:57.760 So, now that we made this clear, what does this line do? 00:00:58.540 --> 00:01:02.860 This line will create an array of three pointers to integers. 00:01:03.640 --> 00:01:08.050 It will maybe look clearer if I move this asterisk next to the data type. 00:01:09.240 --> 00:01:14.480 But what if I put this identifier inside of parentheses together with 00:01:14.480 --> 00:01:18.510 the asterisk? This is no longer an array declaration. 00:01:18.520 --> 00:01:22.000 This is a pointer which points to an array of three 00:01:22.000 --> 00:01:26.980 integers, so this is truly a pointer to an array, not a 00:01:26.980 --> 00:01:29.460 pointer to the first element of the array. 00:01:30.540 --> 00:01:33.290 Since it points to the array with three integers, 00:01:33.300 --> 00:01:37.340 that means that its pointer arithmetic works in increments of 12 00:01:37.340 --> 00:01:41.460 bytes, because 3 integers need 12 bytes in total. 00:01:42.540 --> 00:01:43.030 Okay, 00:01:43.040 --> 00:01:47.550 this kind of makes sense, but what will we get when we dereference this pointer? 00:01:48.340 --> 00:01:49.030 Well, 00:01:49.040 --> 00:01:52.790 if a dereferenced pointer to an integer gives us an integer, a 00:01:52.790 --> 00:01:57.370 dereferenced pointer to an array should give us an array. And this is 00:01:57.370 --> 00:02:01.660 exactly what it does, but since every array name is just a pointer to 00:02:01.660 --> 00:02:03.230 the first element of the array, 00:02:03.240 --> 00:02:06.040 you can think of the result of this expression as a 00:02:06.040 --> 00:02:08.860 pointer to the first element of the array. 00:02:10.240 --> 00:02:13.790 I hope that this makes sense, because I get tangled up in trying to explain 00:02:13.790 --> 00:02:18.350 this terminology of a pointer to an array, because we would sometimes say that 00:02:18.350 --> 00:02:22.050 the pointer is pointing to an array even though we mean the pointer is 00:02:22.050 --> 00:02:24.760 pointing to the first element of that array. 00:02:25.740 --> 00:02:30.360 If you didn't get this, maybe it will become clearer once I use it in practice. 00:02:30.740 --> 00:02:34.500 So, let's say that we need a dynamic array where only the first 00:02:34.500 --> 00:02:39.080 dimension is dynamic. In that case, new operator allows us to 00:02:39.080 --> 00:02:42.060 allocate multidimensional arrays on the heap. 00:02:43.040 --> 00:02:46.910 I could store the memory address from the heap in a simple pointer, but 00:02:46.910 --> 00:02:50.060 I want to store it inside of a pointer to an array. 00:02:50.440 --> 00:02:54.940 Specifically, I want a pointer to an array of three integers, because the 00:02:54.940 --> 00:02:58.360 second static dimension is the array of three integers. 00:02:59.340 --> 00:03:04.860 And now I can use this pointer to access each row by using an offset. 00:03:05.840 --> 00:03:09.520 Since this is a pointer to an array of three integers, and three integers 00:03:09.520 --> 00:03:13.740 need 12 bytes, the pointer arithmetic of this pointer will work with an 00:03:13.740 --> 00:03:19.700 offset of 12 bytes, so adding 1 to this pointer will get us an address of 00:03:19.700 --> 00:03:22.250 the first element from the second row. 00:03:22.740 --> 00:03:26.500 Once we have that, we can use an offset of one integer to get 00:03:26.500 --> 00:03:29.250 the wanted number from the specific column. 00:03:29.640 --> 00:03:32.360 This syntax should look familiar by now. 00:03:32.370 --> 00:03:36.560 You know that we can rewrite this to actually use two square brackets. 00:03:37.440 --> 00:03:41.760 So now we have all of the elements placed in the same block of memory, and we 00:03:41.760 --> 00:03:45.450 can also use the two square bracket syntax to access them. 00:03:45.840 --> 00:03:49.000 But remember that this is only possible if the first 00:03:49.000 --> 00:03:52.050 dimension is dynamic and others are static. 00:03:52.440 --> 00:03:55.290 If I wanted to have another static dimension, 00:03:55.300 --> 00:03:59.830 I can just add it to this declaration. And now I should have a pointer to 00:03:59.830 --> 00:04:03.360 the array that contains all of these static dimensions. 00:04:04.040 --> 00:04:06.220 I can prove this by using auto. 00:04:06.230 --> 00:04:10.050 If I use the auto keyword here and hover over this identifier, 00:04:10.060 --> 00:04:13.550 you can see the type of the pointer that my editor deducted. 00:04:14.640 --> 00:04:18.600 So, to sum up, if you need a static multidimensional array, 00:04:18.610 --> 00:04:23.440 use the regular syntax. If you need all of the dimensions to be dynamic, 00:04:23.440 --> 00:04:27.300 make a simple array and use the formula to manually access elements. 00:04:27.310 --> 00:04:30.460 And if only the first dimension needs to be dynamic, 00:04:30.470 --> 00:04:34.300 you can create a multidimensional array on the heap and use auto to 00:04:34.300 --> 00:04:37.050 deduce the correct type of pointer to an array.