WEBVTT 00:00.830 --> 00:07.660 See some mental model for memory last time and also how to get the address of a variable. 00:07.780 --> 00:17.070 Now I want to talk about pointers so pointers are variables that store the address of other variables. 00:17.080 --> 00:21.210 So here is my mental model for a pointer. 00:21.640 --> 00:31.840 So a pointer is just like any other very well it has an address and that and that value for a pointer 00:31.840 --> 00:36.240 is the address of some other variable. 00:36.280 --> 00:44.010 So the other way I look at it is in the same address but it points to some variable. 00:44.620 --> 00:47.590 That's why we call turret's. 00:47.620 --> 00:57.470 So to actually make a pointer Here's how you do it in each will just make a pointer to an integer and 00:57.560 --> 00:59.710 call my ints pointer 01:02.950 --> 01:04.690 so notice the star. 01:04.690 --> 01:10.010 Here is what really makes it a pointer so points to an integer. 01:10.030 --> 01:18.330 So you can read this from right to left as a pointer to an integer k and we can set its value by using 01:18.330 --> 01:19.930 the address of operator. 01:19.950 --> 01:34.430 So let's make another integer or an actual integer in it 5 and will set the address of x as the value 01:34.430 --> 01:38.020 of the pointer k. 01:38.470 --> 01:45.910 So now the point pointer points to X and its value is the address of x. 01:45.970 --> 01:52.570 So note here that this integer pointer must have the address of an integer. 01:52.600 --> 01:55.720 So it wouldn't work with any other type. 01:55.830 --> 01:58.400 So you might be asking so what. 01:58.410 --> 01:59.990 Why is this useful. 02:00.360 --> 02:10.400 Well I can actually access X through the pointer and have my pointer behave as if it was x. 02:10.410 --> 02:13.510 So C example. 02:13.510 --> 02:19.550 So you can actually say my inch wheelchair 02:24.480 --> 02:29.850 wants to 10 and which is output the value of x. 02:31.110 --> 02:35.330 Alue X is 02:40.180 --> 02:47.210 K and run this and it says the value of x is 10. 02:47.400 --> 02:48.900 But we never set the 02:51.820 --> 02:54.720 value on X directly. 02:54.790 --> 03:04.190 We did it through our my int pointer K and to do this we use what's called the dereference operator. 03:04.200 --> 03:13.110 This star in front of the pointer so when you dereference the pointer the point you're kind of takes 03:13.110 --> 03:15.340 on what it points to. 03:16.230 --> 03:21.630 The dereference operator can be read as value pointed to by. 03:22.110 --> 03:29.820 So the value pointed to by my end pointer is equal to 10. 03:29.960 --> 03:32.430 Sort of how you read that. 03:32.450 --> 03:40.250 So once the pointer is the reference type needs to be known Remember that the type that the pointer 03:40.250 --> 03:49.280 points to is not the type of pointer itself when important new key word that I use with pointers is 03:49.280 --> 03:51.420 called null pointer. 03:51.800 --> 03:58.250 So here if I set this to no pointer 04:02.460 --> 04:07.260 this can actually set in 04:09.770 --> 04:11.200 wintered here. 04:13.240 --> 04:18.870 X just so it doesn't blow up. 04:19.000 --> 04:24.590 So this statement here. 04:25.000 --> 04:30.690 This means that this my end pointer points to nothing. 04:31.000 --> 04:38.740 So null pointer is really a special place in memory that contains nothing. 04:38.750 --> 04:47.600 So one important note is if your pointer is pointing at null pointer dereferencing your pointer like 04:47.630 --> 04:48.500 this. 04:48.500 --> 04:55.030 Let's say my int pointer goes to 10 let's say. 04:55.170 --> 04:59.310 So let's try this. 04:59.370 --> 05:02.170 So it didn't really work. 05:02.210 --> 05:07.690 I think Straten time time is that value. 05:07.690 --> 05:09.050 Negative one. 05:09.280 --> 05:10.560 So it didn't work. 05:11.100 --> 05:21.190 And that is because dereferencing something or when you dereference this pointer you're obtaining the 05:21.190 --> 05:25.750 reference type but no pointer has no type. 05:25.840 --> 05:27.790 It's kind of undefined behavior. 05:27.790 --> 05:31.740 So that's why you're kind of seeing nothing really happening here. 05:32.260 --> 05:34.660 So that's something you have to avoid. 05:34.660 --> 05:36.030 So never do that. 05:37.380 --> 05:41.970 So in the next lecture I'll talk about a similar concept called reference's.