WEBVTT 00:00.330 --> 00:05.190 Hello again! In this video, we are going to have a practical demonstration of lambda expressions. 00:05.760 --> 00:11.280 I am going to take the equal_strings function we wrote earlier in the course and rewrite that, using 00:11.280 --> 00:13.980 an algorithm and a lambda expression. 00:15.990 --> 00:22.260 We wrote the equal_strings function in the video on Character Functions. It takes two string arguments, 00:22.530 --> 00:26.730 and it compares each character in the string, after converting them to uppercase. 00:28.290 --> 00:32.310 So here is the code, which we have seen before. 00:35.610 --> 00:38.010 We have a test() function and a main(). 00:39.900 --> 00:45.120 So this will ignore differences in the case, but it will not ignore different characters. 00:45.750 --> 00:47.790 We are going to use the equal() algorithm. 00:48.150 --> 00:50.640 This compares the elements in two containers. 00:51.240 --> 00:56.730 It takes 4 arguments: an iterator range for the first container, and an iterator range for the 00:56.730 --> 00:59.100 second container, and it returns bool. 00:59.760 --> 01:04.800 This will go through and compare each element in the first container with the corresponding element 01:04.860 --> 01:12.990 in the second container. As soon as it encounters a discrepancy - a mismatch - it returns false. If it gets 01:12.990 --> 01:15.690 through the first container without finding any mismatches, 01:16.110 --> 01:17.370 then it returns true. 01:18.300 --> 01:22.980 If the first container has more elements, it returns false, regardless of the data. 01:23.760 --> 01:28.320 If the second container has more elements, then those extra elements are ignored. 01:30.270 --> 01:36.450 By default, this will use the equality operator to compare the elements. And if the containers are 01:36.450 --> 01:42.000 strings, then that means it is going to do a case-sensitive comparison of each character in the string. 01:43.950 --> 01:50.100 There is an overload of the equal algorithm, which takes a callable object as an optional extra arguments. 01:50.730 --> 01:56.100 And we can use this predicate to change the way that the equal() function compares the elements. 01:57.870 --> 02:03.510 This predicate is going to be called instead of the equality operator so we can make this do whatever 02:03.510 --> 02:07.230 we want for - to change the criteria for equality. 02:08.860 --> 02:13.660 In our example, we want two characters to be equal if they have the same value after being converted 02:13.660 --> 02:14.530 to uppercase. 02:17.700 --> 02:22.920 The lambda expression is going to be called with one character from each of the two strings. Then we 02:22.920 --> 02:29.640 convert each character to uppercase. And then we compare them, and we return true or false, depending 02:29.640 --> 02:30.950 on whether they are equal or not. 02:31.350 --> 02:31.920 And that is it! 02:33.270 --> 02:37.350 So here is the version with the lambda expression. You will notice this is much shorter. 02:37.650 --> 02:44.100 The entire program fits on a single screen (almost!), whereas before the equal_string() function took up 02:44.100 --> 02:44.970 an entire screen. 02:46.050 --> 02:48.000 So here is the equal strings function, 02:48.000 --> 02:51.090 again. It just calls the equal() algorithm. 02:51.780 --> 02:55.410 So we pass the iterator range for the two string arguments. 02:56.070 --> 02:59.520 The first string and the second string argument. 03:00.240 --> 03:05.490 Then we have our lambda expression, which takes a character from each string. And then, in the body, 03:05.490 --> 03:11.310 we convert the characters to uppercase and compare them. And the rest of the program is the same. 03:14.860 --> 03:15.490 And there we are. 03:19.000 --> 03:24.970 So the advantage of this is, we replaced a screen full of code, with lots of things that could go wrong, with 03:24.970 --> 03:26.440 just one simple statement. 03:26.920 --> 03:32.830 And perhaps this statement is quite complex if you are not used to it, but it does become second nature. 03:33.070 --> 03:39.040 You can actually format it slightly differently, to make it a bit easier to read. Depending on your 03:39.040 --> 03:39.400 style. 03:40.810 --> 03:42.460 OK, so that is it for this video. 03:42.880 --> 03:45.700 I will see you next time, but until then, keep coding!