WEBVTT 00:00.480 --> 00:05.190 Hello again! In this video, we are going to look at the equality and inequality operators. 00:07.120 --> 00:13.930 The equality operator takes two objects of the same type and returns a bool. We invoke it by putting a equals 00:13.930 --> 00:18.820 equals b, and it will be called as operator equals equals with arguments a and b. 00:19.750 --> 00:23.800 The return value should be true when the two objects are equal. 00:24.250 --> 00:30.490 So, whatever that means for two objects of the class to be equal. And if they are not equal, then it returns 00:30.490 --> 00:39.280 false. the inequality operator is the not equals operator, and the return value is obviously the other 00:39.280 --> 00:39.790 way round. 00:40.060 --> 00:42.790 If the two objects are equal, it returns false. 00:43.450 --> 00:44.950 Otherwise, it returns true. 00:49.510 --> 00:55.000 If a class defines one of these operators, it probably also needs to define the other one, which 00:55.000 --> 00:55.720 is trivial. 00:56.560 --> 01:02.650 You can just implement the inequality operated by calling the equality operator, and inverting the result. 01:03.280 --> 01:06.070 So here we have the arguments of the inequality operator. 01:06.610 --> 01:10.810 We compare them, and if they are equal, we return false. 01:10.810 --> 01:12.700 And if they are different, we return true. 01:14.700 --> 01:18.990 We are going to demonstrate this with a basic class for a student. 01:19.530 --> 01:24.960 So the student has a name and an identity number, and perhaps some other data and member functions that 01:24.960 --> 01:27.090 we are not really interested in for this example. 01:29.010 --> 01:31.890 So what does this actually mean for two students to be equal? 01:32.940 --> 01:34.200 Does it mean they have the same name? 01:34.440 --> 01:35.820 Well, not necessarily. 01:35.850 --> 01:41.670 You can have two different people who have the same name. But the university or the college, or whatever, 01:41.850 --> 01:44.670 does make sure that each student's ID number is unique. 01:45.090 --> 01:47.250 So that is going to be different for each students. 01:47.790 --> 01:51.720 So if we compare the name, we may get some false results. 01:51.720 --> 01:54.750 We may think that two different students with the same name are the same person. 01:55.260 --> 01:58.320 If we compare the ID's, we will never get these false results. 01:58.890 --> 02:01.920 So here is our student class with the name and the ID. 02:02.820 --> 02:07.890 I have been a bit lazy and used the friend keyword for the operators, but I have actually written it 02:07.890 --> 02:10.290 out as a separate header and source file. 02:10.290 --> 02:12.210 So it is not all bad news :) 02:13.830 --> 02:17.880 And there is also a print member the function for displaying the private data. 02:20.280 --> 02:23.640 And then, in the source file, we define these functions. 02:23.640 --> 02:28.350 We have the equality operator, the inequality operator and the print function. 02:30.150 --> 02:35.500 And there is also a separate main() in which we create some student objects. 02:35.520 --> 02:38.940 So we have two students with the same name, just to check how that works. 02:39.150 --> 02:46.050 But with different ID's. And then a completely different student. Then we print out the details and 02:46.050 --> 02:49.530 we print out the results of comparing them. 02:50.460 --> 02:51.560 So let's see what happens. 02:55.350 --> 03:01.170 So we have two John Smiths, but they have different ID's, so they are regarded as different people. 03:01.920 --> 03:04.470 Obviously, John Smith and Jack Jones are going to be different. 03:05.730 --> 03:09.810 So that is all right. If we go to the student.cpp and change this. 03:09.810 --> 03:11.700 So we are comparing the names. 03:17.850 --> 03:23.250 And then it thinks that the two John Smiths are the same person, which is not the right way to do it. 03:23.460 --> 03:29.430 So sometimes you need to stop and think a bit about what it actually means, for two objects of your class 03:29.430 --> 03:30.210 to be equal. 03:30.690 --> 03:32.730 The obvious comparison might not always be the correct one. 03:33.660 --> 03:35.580 Okay, so that is it for this video. 03:35.910 --> 03:38.880 I will see you next time, but until then, keep coding!