WEBVTT 00:00.640 --> 00:05.800 We are at the end of this section so we should be doing some practice. 00:05.820 --> 00:13.940 So start with problem one says read phrase from the user and output it again. 00:14.310 --> 00:23.610 So typically what we've been doing so far is just sort of reading one thing from the user and then kind 00:23.610 --> 00:30.390 of using that or maybe a couple things string together say a couple of integers with spaces in reading 00:30.390 --> 00:38.000 those but we haven't really done that with entire phrases so want to show how that works here. 00:38.400 --> 00:48.810 So to start this we will see you need a buffer or an array of characters. 00:49.030 --> 00:49.760 OK. 00:50.270 --> 00:52.660 Is usually called the buffer. 00:52.770 --> 00:57.050 It's just another name for Array. 00:57.310 --> 01:08.330 It's going to be some length and does really matter too much but just enough in words call it buffer 01:09.470 --> 01:11.630 say Max buffer. 01:13.700 --> 01:24.150 It's going to be a character array with 256 characters or Max buffer length characters responses. 01:24.240 --> 01:29.720 The ouch ease enter phrase. 01:31.680 --> 01:48.470 This and how we get sort of a bigger string of characters is through this get CNM get function and we 01:48.470 --> 02:00.030 pass it our buffer which is in an array and the max number of characters. 02:00.080 --> 02:00.910 OK. 02:01.200 --> 02:12.230 And it'll actually be minus one because actually what happens and I get will get the all the characters 02:12.650 --> 02:16.540 and then add a null character at the end. 02:17.270 --> 02:17.810 OK. 02:17.900 --> 02:23.200 So that's why we need to have it be minus one. 02:23.280 --> 02:34.130 I mean to account for the null character that will be added K and all we have to do now is output it. 02:34.180 --> 02:38.740 So your input is 02:41.490 --> 02:42.990 just a buffer. 02:46.680 --> 02:57.570 If you're on this say hello to everyone this and your input was Hello everyone's what worked. 02:57.720 --> 03:07.290 So what it did was it actually read 256 characters or up to the new line character. 03:07.290 --> 03:07.560 Right. 03:07.570 --> 03:11.580 So you have to press enter to finish it. 03:11.580 --> 03:16.340 So just read your 256 characters or up to the new. 03:16.340 --> 03:19.500 I just like how I see and ignore it. 03:19.530 --> 03:21.790 If you remember. 03:22.620 --> 03:25.130 So that's it for that question. 03:25.440 --> 03:29.140 And you'll notice that this one didn't have anything to do with dynamic memory yet. 03:29.400 --> 03:31.440 This one will. 03:31.440 --> 03:41.580 So using Problem 1 Make a function that will take in the input phrase and returns the reverse copy of 03:41.580 --> 03:43.280 the phrase and outputs. 03:44.110 --> 03:54.980 OK so we're going to use a function and it's going to return a character a race a new character a race 03:55.030 --> 04:03.330 a whole new bunch of memory from the heap and return you a character pointer to that the new memory 04:03.760 --> 04:06.240 going to call it reverse. 04:06.330 --> 04:12.940 Copy this and it's going to take a C string 04:15.700 --> 04:16.700 and that's it. 04:16.720 --> 04:19.000 In fact it's going to take this string. 04:19.000 --> 04:19.490 Right. 04:19.650 --> 04:26.050 So remember the difference between a character array and a C string is that C string has the no character 04:26.050 --> 04:27.020 at the end. 04:27.110 --> 04:34.070 And they just said that get well actually insert no character into our array. 04:34.490 --> 04:35.110 OK. 04:35.470 --> 04:37.930 So that's why it's going to be a C string. 04:38.380 --> 04:40.030 So that's why we don't need length here. 04:40.050 --> 04:45.070 If it was just a regular array we'd one length but we don't need that here. 04:45.640 --> 04:55.570 So it's copy that. 04:55.660 --> 05:01.020 So what's go well we actually will need the length. 05:01.020 --> 05:03.600 But when you take the length in a different way. 05:03.740 --> 05:04.510 OK. 05:04.840 --> 05:10.910 So let's say it's actually just use it. 05:10.930 --> 05:12.390 See what it looks like. 05:12.430 --> 05:13.530 Sure. 05:14.360 --> 05:16.950 Stars are busy owning pointer. 05:17.050 --> 05:17.510 OK. 05:17.550 --> 05:24.840 So this is going to reverse copy will actually make a new new array pointer. 05:25.070 --> 05:38.960 So it's going to call it a reverse for AIDS Let's say I call it a reverse copy where it passes the buffer. 05:41.100 --> 05:45.640 We're going to use out. 05:46.010 --> 05:48.140 Let's just say that Free's 05:50.760 --> 05:57.530 is to print out the E-string 06:01.090 --> 06:03.580 this. 06:03.840 --> 06:12.500 And since we own the pointer we should be the one who deletes delete pointer. 06:12.620 --> 06:15.560 Freezing this OK. 06:15.580 --> 06:21.940 So that will be our usage of this reverse copy function but now we have to implement it. 06:22.120 --> 06:29.920 So to make this easier since we have to make error verse actually will need the length and I'm going 06:29.920 --> 06:39.520 to use a different function for this and it's going to be I mean we could implement our own string like 06:39.520 --> 06:48.520 function but we need to actually because there is a function called strollin and it's part of kind of 06:48.630 --> 06:51.580 the C++ standard. 06:51.970 --> 06:58.790 But we need to include something called C string. 06:58.820 --> 07:04.710 So if you include C string you get this function to use this function. 07:04.870 --> 07:07.870 So the sloshy get the length of this 07:10.480 --> 07:17.670 and let's say it's actually make our reverse string 07:20.120 --> 07:30.280 that's new dher of and it should be how long. 07:30.700 --> 07:40.190 Well if we know how long the phrase is than it should be the length of the phrase plus one and it's 07:40.190 --> 07:45.400 plus one for the no character. 07:45.570 --> 07:51.920 And so we always have to have one extra spot for that no character. 07:53.220 --> 07:57.930 And or indeed a j variable that says from J. 07:57.940 --> 07:59.460 Close to zero. 07:59.460 --> 08:01.500 See why in a second. 08:01.500 --> 08:05.000 And are you going to loop in reverse for this one. 08:05.010 --> 08:09.770 So I say at length and ask me minus one. 08:11.580 --> 08:20.590 This will be the end of the phrase right and this is the last character of phrase. 08:21.230 --> 08:27.090 And as long as it's greater than or equal to zero I minus minus. 08:27.090 --> 08:35.730 And so we're going kind of backwards through the array and then we say reverse and we'll see. 08:35.760 --> 08:38.160 J This is why we have J. 08:38.280 --> 08:43.610 Because we're going to go forward in the reverse array. 08:43.830 --> 08:48.620 But we're going to go backwards in the phrase or a. 08:48.720 --> 08:51.430 So this one gets high instead. 08:51.810 --> 08:55.080 And then we're increment J this 08:57.790 --> 09:02.340 straight she. 09:03.080 --> 09:08.590 And then we're quite done with reverse string reverse string. 09:08.720 --> 09:16.280 J is equal to the null character because this is a C string and we know it will be at J because once 09:16.280 --> 09:24.290 this is done once it's on the last character this will be incremented sort of kind of point one past 09:24.290 --> 09:25.790 the last character. 09:25.790 --> 09:31.940 So will be pointing at this the length minus or plus 1. 09:31.970 --> 09:34.800 Essentially index. 09:34.830 --> 09:39.990 So then we know we can just use J here k. 09:40.150 --> 09:48.030 It's pointing at the very end anyway and we just sign that to the null character and we just say turn 09:49.660 --> 09:53.160 over string this. 09:53.350 --> 09:54.940 So if you run this 09:59.300 --> 10:02.080 I say hello to you on 10:05.140 --> 10:07.550 this. 10:07.710 --> 10:10.260 And so your input was. 10:10.260 --> 10:11.680 Hello everyone. 10:11.720 --> 10:14.530 Very formatted very nicely. 10:15.240 --> 10:15.700 This 10:18.760 --> 10:19.180 around that 10:22.480 --> 10:31.980 on gay or it was Hello everyone and the phrase Well the reverse of the phrase is right. 10:31.990 --> 10:36.410 You know all this they kind of read it backwards. 10:36.880 --> 10:39.860 So that gives you the reverse. 10:39.910 --> 10:46.690 So in the next section you're going to use what we learn right here to apply to hang man. 10:46.980 --> 10:48.680 It will be our second game. 10:48.860 --> 10:50.710 So I'll see you in the next section.