WEBVTT 00:00.610 --> 00:03.430 We've seen the usage of pointers with variables. 00:03.430 --> 00:12.010 Up until this point and just like variables functions also have a specific address in memory. 00:12.310 --> 00:20.620 We can exploit this fact and actually have pointers that point to functions and they're called function 00:20.620 --> 00:22.120 pointers. 00:22.120 --> 00:27.330 So here's how to actually make a function pointer. 00:27.410 --> 00:42.700 So we have the function and say return type here and in these parentheses we have the star and whatever 00:42.700 --> 00:53.150 the function pointer you want things function pointer and these parentheses will actually be the argument 00:53.380 --> 00:56.270 just OK. 00:56.640 --> 01:03.740 So you can actually make a function pointer with a specific signature. 01:03.740 --> 01:11.090 So this so the signature will really depend on what the argument list is and what the return type is. 01:11.090 --> 01:13.960 And we can actually have mentors that point to it. 01:13.970 --> 01:17.400 So let's see an example of this. 01:17.600 --> 01:26.790 That's And let's say we had a function that took the sum of some array. 01:27.090 --> 01:39.070 This in the like A and let's say we had a similar function that said where are we in terms of the signature 01:39.790 --> 01:43.960 and that the average the rate 01:46.760 --> 01:48.440 the length ears wow 01:51.550 --> 02:02.020 and let's say we also had one other function and say it's the output and it's going to take the array 02:02.890 --> 02:03.670 and the length 02:07.210 --> 02:12.030 and it's actually going to take a function pointer 02:15.850 --> 02:17.200 like it's 02:20.150 --> 02:21.040 the array 02:24.230 --> 02:27.020 in one way. 02:34.240 --> 02:38.380 So this output function actually has three arguments. 02:38.440 --> 02:48.190 Has the array has the length of the array and it has this thing which is a pointer to a function K and 02:48.190 --> 02:58.060 that pointer to a function must have as its return type an integer and must have as its arguments an 02:58.060 --> 03:01.850 array and the length k. 03:02.160 --> 03:05.190 So you can kind of see where I'm going with this. 03:05.190 --> 03:12.900 Both of our functions have as the arguments the length and the array and both of them also return an 03:12.900 --> 03:14.220 integer. 03:14.280 --> 03:20.070 So let's implement these implement these first two or simplest 03:22.920 --> 03:44.020 and some will be simple some Sphero sleep over this this like a sports and some sequels array of 03:47.180 --> 04:00.750 which you turn the song and for average all we have to do is get some of the re link here. 04:01.320 --> 04:06.410 And we just divide it by the way Frank. 04:06.480 --> 04:09.490 So those are those two functions. 04:09.750 --> 04:12.130 And now this output function. 04:12.140 --> 04:15.390 So copy this 04:18.580 --> 04:25.470 piece here and this will do is output the results of whatever we pass into it. 04:25.470 --> 04:36.670 So the results is and how you use the function pointer is you just say the name of the function pointer 04:36.910 --> 04:37.750 is a function. 04:37.750 --> 04:46.010 In this case and we pass it the these two arguments. 04:46.270 --> 04:52.410 So these these these arguments just define what the function pointer has as its are you in. 04:52.420 --> 04:54.890 It's not the arguments itself. 04:55.300 --> 05:01.190 So these are the arguments themselves which passed like this. 05:03.180 --> 05:06.370 And all their K. 05:06.800 --> 05:10.630 And now how to use this output function. 05:10.650 --> 05:25.150 So to re say it's the even numbers 2 4 6 8 10 10. 05:25.150 --> 05:33.840 So now if we want to use help we just output array and the like. 05:33.880 --> 05:34.770 5. 05:34.790 --> 05:38.460 In this case and let's say the sup. 05:38.480 --> 05:43.110 So notice I'm using just the name of the function k. 05:43.190 --> 05:48.190 So this is kind of like the address of it and use the name instead. 05:48.380 --> 05:50.860 And notice I'm not using any kind of argument list. 05:50.860 --> 05:52.910 This just is really just the name. 05:53.480 --> 06:00.380 And here I'll also do it for the average. 06:01.130 --> 06:04.090 This right. 06:04.800 --> 06:15.290 So this is doing is it's actually passing the address of the function to this output function here. 06:15.380 --> 06:22.960 So passing it to here and it's actually calling the correct function. 06:23.310 --> 06:30.060 So the first case would be some so would be passing some as the function and I would actually call some 06:30.060 --> 06:31.920 here. 06:32.010 --> 06:40.700 And so this is actually call some and it would do everything that some did and output the sum and do 06:40.730 --> 06:46.130 the same thing with the average So let's do this and see what happens. 06:47.080 --> 06:49.810 So the result is 30. 06:49.810 --> 06:59.320 So in this case we're just adding two four six eight ten which equals 30 and we're actually outputting 06:59.440 --> 07:08.130 the sum using this function pointer and the next one 6 so the average of all this is 6. 07:08.140 --> 07:08.910 Makes sense. 07:09.160 --> 07:10.270 The middle one right. 07:11.680 --> 07:21.490 And it's outputting by calling average down here and using the array and the length actually calls this 07:21.490 --> 07:25.720 function and does all this. 07:26.100 --> 07:32.310 So function pointers are they can be quite useful in some contexts. 07:32.350 --> 07:41.130 We will be really using them in in the next game we have which is battleship but we will use a similar 07:41.130 --> 07:45.460 concept to function pointers and Space Invaders later on. 07:45.480 --> 07:53.800 So I just want to show you this kind of interesting way you can use pointers to functions. 07:54.540 --> 07:56.830 They really do come in handy in some contexts. 07:56.850 --> 08:01.660 And in fact we'll see one of those in the practice in Dr..