WEBVTT 00:00.750 --> 00:06.390 So far we've only been using one kind of memory which is stack memory. 00:06.660 --> 00:13.130 When we create a variable in a function the variable only lives for the lifetime of that function. 00:13.910 --> 00:21.200 When a function finishes all the memory of that function is destroyed stack memory is really a special 00:21.200 --> 00:28.970 region of your computer's memory that stores temporary variables created by each function including 00:28.970 --> 00:30.820 the main function. 00:30.840 --> 00:36.580 We're not going to go over what the stack really is and how it operates. 00:36.600 --> 00:41.160 It's not really all that relevant for this specific course. 00:41.690 --> 00:51.930 Just know that memory for our variables gets destroyed or deallocated when the function finishes. 00:51.930 --> 00:59.260 There's a different way we can create variables and then is through what's called the heap the heap 00:59.270 --> 01:07.540 is essentially a bunch of memory that can be dynamically used by our program. 01:07.710 --> 01:15.290 However it's lifetime is not tied to any functions lifetime it's deallocated when we the programmer 01:15.330 --> 01:23.430 deallocated me potentially it can potentially live for as long as the program itself. 01:23.430 --> 01:30.780 In other words though all the memory you allocate from the heap will be recovered by the OS once your 01:30.780 --> 01:33.850 program actually finishes its execution. 01:34.880 --> 01:40.050 This is called heap allocation or dynamically allocated memory. 01:40.190 --> 01:47.990 It's very useful for when you want to be more flexible about the size of memory that you need. 01:48.050 --> 01:56.840 For example arrays in our last section you had to specify how big the array was beforehand say we need 01:56.840 --> 02:02.490 to hold a bunch of characters but we didn't know beforehand how many won't. 02:02.540 --> 02:08.810 One way we could do is just to make an array that had more than enough characters that we needed say 02:08.810 --> 02:10.200 a thousand. 02:10.340 --> 02:14.950 But what if we only ever needed 100 in practice. 02:14.960 --> 02:19.730 Well our array isn't very flexible and we'd be wasting a bunch of memory. 02:19.820 --> 02:22.120 About 90 percent in this case. 02:22.580 --> 02:28.120 Well instead we could allocate the proper amount each time from the heap. 02:28.130 --> 02:32.830 So here's how we can dynamically allocate memory. 02:32.940 --> 02:50.070 So it's always going to be tied to a pointer so we knew it's a pointer and we say new it can. 02:50.260 --> 02:59.810 So what this did was to get an integer from the heap and said it to our new into pointer to do this 02:59.840 --> 03:08.180 we use the new keyword new will actually fetch memory from the heap and return it as a pointer to that 03:08.180 --> 03:09.890 new memory. 03:09.890 --> 03:15.100 So in this case it fetched an integer from memory so about 4 bytes. 03:15.500 --> 03:24.410 Then we can use either new integer just like we do with any other pointers so I could say new ints Winter 03:24.910 --> 03:30.830 calls to 8 or something like that help put it. 03:30.950 --> 03:44.160 So the value of mine you did for us you it's Peter this. 03:44.280 --> 03:45.340 We run it. 03:46.920 --> 03:48.510 We eat. 03:49.110 --> 03:56.720 But like I said in the last lecture this memory won't go away after the end of the function. 03:58.090 --> 04:03.940 So how do we get rid of the memory when we're finished so we're not actually getting rid of the memory 04:04.000 --> 04:04.430 yet. 04:04.450 --> 04:11.740 Although like I said when the program is finished executing all our memory will be deallocated for us 04:11.740 --> 04:25.540 anyways but if we want to sort of do this a bit more properly what we do is we say delete new pointer 04:27.280 --> 04:36.750 OK so the delete key word will put the memory that you got from the heap and it will return it to the 04:36.750 --> 04:37.190 heap. 04:37.200 --> 04:44.300 So how you read this is delete the memory pointed to by new into pointer. 04:44.480 --> 04:47.270 OK so you should read this. 04:47.340 --> 04:50.510 So this is always good practice to do. 04:50.520 --> 04:56.020 You should always delete the memory you took from the heap when you're done with it. 04:56.080 --> 05:00.000 So how to do this with arrays in the next lecture.