WEBVTT 00:00.410 --> 00:00.710 Okay. 00:00.710 --> 00:05.210 So let's talk about another control structure the switch statement. 00:05.390 --> 00:09.080 Let me create the switch PHP file. 00:09.230 --> 00:14.360 Add a PHP tag and let's see what is this about. 00:14.390 --> 00:22.190 So switch statement is very similar to the if statement but there are some differences. 00:22.220 --> 00:25.130 Let me start with an example. 00:25.130 --> 00:29.660 And we're gonna see how it differs from an if statement. 00:30.380 --> 00:35.180 So as an example here I'd like to use that t shirt sizes. 00:35.180 --> 00:44.210 And we're just gonna evaluate the value of the size variable and output the text that will describe 00:44.210 --> 00:48.140 this size based on the size variable value. 00:48.170 --> 00:55.760 So let's start with the switch statement which begins with the switch keyword and the parentheses. 00:55.760 --> 00:57.500 There goes the expression. 00:57.500 --> 01:05.180 So the first difference with the if statement is that in the if statements, you add an expression that 01:05.180 --> 01:12.920 is being evaluated to Boolean, and if this is true, then you run the code inside the if statement 01:12.920 --> 01:20.150 body or any of the alternatives when you use the else if with switch, there is a different logic to 01:20.180 --> 01:20.840 this. 01:21.380 --> 01:23.960 You add an expression to the switch statement. 01:23.960 --> 01:31.730 So here we're gonna evaluate the actual value of size, not whether it is true or false. 01:31.730 --> 01:43.430 And then you just add cases like you add a case where the value is m and you echo that this is small 01:43.430 --> 01:45.710 or medium size. 01:46.820 --> 01:59.180 So corresponding if statement would be if m equals size then you'd like to echo this text. 02:00.050 --> 02:08.180 So the text I've echoed here is small or medium size, which means I'd like to echo the same text if 02:08.180 --> 02:10.970 the size is either medium or small. 02:11.000 --> 02:18.260 So with the switch statement, I can handle both cases by adding another case statement and check if 02:18.260 --> 02:22.280 the value of size is either s or m. 02:23.540 --> 02:34.670 So the corresponding if statement is whether m equals size or whether s equals size. 02:37.010 --> 02:37.280 Okay. 02:37.280 --> 02:40.880 So now let's handle the large and XL sizes. 02:40.880 --> 02:43.790 So for that I can also paste this code. 02:43.790 --> 02:47.270 And there I add L and XL. 02:47.270 --> 02:53.420 And I say large or extra large size. 02:53.990 --> 03:02.780 Now if the size is unknown There is something similar to Els in if, which would be the default case 03:02.780 --> 03:03.890 which is run in. 03:03.920 --> 03:10.910 If none of the above cases match, so then I echo unknown size. 03:10.940 --> 03:15.080 Now let me add a corresponding one if statement. 03:16.130 --> 03:18.920 Now let me add a corresponding if statement. 03:18.920 --> 03:21.470 So here I would have to. 03:26.390 --> 03:29.300 Now let's add a corresponding if statement. 03:29.570 --> 03:40.130 So I'm adding an else if and checking for large or extra large and echoing this text. 03:41.240 --> 03:48.680 Then I also need an else alternative where we echo dot text. 03:48.770 --> 03:52.610 So as we see there are some differences. 03:52.610 --> 04:00.620 Maybe there is more lines of code with the switch statement, but other than that, it all boils down 04:00.620 --> 04:04.190 to the preference of which one you would prefer. 04:04.280 --> 04:13.340 So now let's go to some unique features of switch that really differs this statement from the if statement. 04:14.360 --> 04:15.950 So it's time to run this. 04:15.980 --> 04:19.340 I'm going to add a new line character to all those strings. 04:19.340 --> 04:22.820 So it's clearly visible in the output. 04:22.820 --> 04:28.490 And I think you might be a little bit surprised with the output of this. 04:28.490 --> 04:32.000 So we are running both switch and if statements. 04:32.090 --> 04:35.360 So let me run PHP switch PHP. 04:35.870 --> 04:37.640 So this is the output. 04:37.640 --> 04:43.610 We got small or medium size but also the large also the unknown size text. 04:43.610 --> 04:46.340 And then again small or medium size. 04:46.340 --> 04:53.570 So what happened here is this three lines come from the switch statement and the last one from the if 04:53.570 --> 04:54.290 statement. 04:54.290 --> 04:59.990 And that's a big difference with how the switch and if statements behave. 05:01.640 --> 05:03.620 So first the if statement. 05:03.650 --> 05:11.090 In this case you just check for some conditions and only then you run the code that is under this condition. 05:11.090 --> 05:15.710 So it is either this or this or that. 05:15.740 --> 05:22.880 You can't run a couple of those statements from different conditions because they are mutually exclusive, 05:22.910 --> 05:25.340 unless your conditions are the same. 05:25.370 --> 05:29.750 Now with the switch statement it works a little bit different. 05:30.170 --> 05:38.000 So the way switch statement works is given the expression it tries to find a matching case. 05:38.000 --> 05:40.220 So in our case that's M. 05:40.220 --> 05:45.710 And this first case is already matching the value of size. 05:45.710 --> 05:47.810 So this statement was run. 05:47.810 --> 05:53.030 But what happened next is all the other statements were run as well. 05:53.030 --> 05:57.890 This is a kind of a fallback nature of the switch statement. 05:57.920 --> 06:04.430 Now, if you don't want this to happen, you would need to add a break statement after every single 06:04.430 --> 06:05.030 case. 06:05.030 --> 06:06.650 We're gonna do that in a second. 06:06.650 --> 06:13.220 But first, let me change the size to L so that the first case won't match. 06:14.750 --> 06:17.720 Now let's run the switch PHP script. 06:17.720 --> 06:22.010 And now we see that we only got the large or extra size. 06:22.010 --> 06:28.160 But then the also default case, the unknown size and the if statement stays the same. 06:28.160 --> 06:35.150 It only echoes one text because it can only match one condition. 06:37.430 --> 06:43.640 So if we would like the switch statement to behave like the if statement after every single one of those 06:43.640 --> 06:50.960 cases, we need to add a break statement except the default one, because that's the last one. 06:50.960 --> 06:53.180 Nothing else will run after it. 06:53.180 --> 07:01.790 So the way it would work right now is if the switch statement will find a matching case for whatever 07:01.790 --> 07:09.020 expression you evaluate, like let's say this one, the large size, it will run all the statements 07:09.020 --> 07:10.130 that you have right here. 07:10.130 --> 07:13.910 And then it will break this switch statement. 07:13.910 --> 07:17.750 It will exit it so no other cases will be run. 07:18.890 --> 07:26.480 So let's see that now we have the exactly the same behavior of the if and switch statements. 07:26.660 --> 07:33.470 So it seems that with the switch statement, we just need to write a lot more code than with the if 07:33.470 --> 07:34.040 statement. 07:34.040 --> 07:39.230 And maybe that's the reason why the switch statement is less popular. 07:39.230 --> 07:45.470 But actually this behavior of the switch statement is for a reason. 07:45.470 --> 07:47.780 So maybe let's see another example. 07:47.780 --> 07:53.220 When this behavior of switch statement will make a lot more sense. 07:54.450 --> 08:02.220 Now to discuss this behavior of the switch statement, I would like to jump to Stack Overflow because 08:02.220 --> 08:04.980 I found this interesting discussion here. 08:05.250 --> 08:06.660 It's about C plus plus. 08:06.660 --> 08:13.230 But essentially the switch statement is exactly the same in PHP like in C plus plus. 08:13.230 --> 08:20.880 And people discuss the nature of switch statement and including the break and how it behaves without 08:20.880 --> 08:21.420 it. 08:21.570 --> 08:30.210 And this statement is interesting that not using break statement is generally considered a bad practice, 08:30.210 --> 08:33.510 but sometimes it may be handy. 08:33.540 --> 08:42.450 Well, I've also heard that not using break statement is sometimes considered a bad practice, but we 08:42.450 --> 08:48.870 also have to think that if this would be a bad practice, why would this be part of the language? 08:48.870 --> 08:51.090 Why would this be even allowed. 08:51.090 --> 08:54.690 So I think it might be. 08:54.690 --> 08:59.400 Maybe I'm gonna call it controversial that this is possible. 08:59.400 --> 09:03.000 And that's the way just the switch statement works. 09:03.000 --> 09:05.310 It has this fall back nature. 09:05.310 --> 09:13.170 I think this here is a great example of why not using the break statement might be beneficial. 09:13.170 --> 09:21.390 So here you've got the amount of bad login attempts when someone tried to log in and failed. 09:22.830 --> 09:25.410 So you go from top to bottom. 09:25.410 --> 09:32.850 If someone already tried three times you do something, you alert the admin, you block the account. 09:32.880 --> 09:37.200 Doesn't matter what this does exactly, but then you don't break. 09:37.230 --> 09:40.290 You always execute the next statements. 09:40.290 --> 09:48.090 If there were only two bad attempts at signing in, logging in, and one attempt, and then you always 09:48.090 --> 09:52.530 log this error and increase the number of bad attempts. 09:52.530 --> 09:55.920 So it's something like do it all the time. 09:55.980 --> 10:03.900 And in some special cases, like higher up cases, also do some additional things. 10:07.050 --> 10:07.350 Okay. 10:07.350 --> 10:09.990 So let's also try to implement this example. 10:09.990 --> 10:13.200 Let's define the bad attempts variable. 10:13.200 --> 10:15.120 Initialize it with two for now. 10:15.240 --> 10:22.050 Then let me add a switch statement that evaluates this bad attempts. 10:22.050 --> 10:24.900 And essentially you just need to put an expression here. 10:24.930 --> 10:26.700 Doesn't have to be a variable. 10:26.700 --> 10:28.830 And then let's add the cases. 10:28.830 --> 10:30.690 So we start with three. 10:30.690 --> 10:37.950 And then I'm just going to echo something here that you are blocked. 10:39.690 --> 10:42.660 But then we also need to handle the other cases. 10:42.660 --> 10:50.820 So we don't necessarily in this case need to add two and one because just a default case would be enough. 10:51.780 --> 10:52.830 But let's add it. 10:52.830 --> 10:56.040 So case two and case one. 10:56.040 --> 11:02.490 So if the value of bad attempts is either 2 or 1 we log it. 11:02.520 --> 11:06.780 That bad attempt detected. 11:10.380 --> 11:11.190 And that's it. 11:11.220 --> 11:14.610 So let's now see how this would behave. 11:15.600 --> 11:18.570 So let's run the switch script. 11:18.840 --> 11:19.140 Okay. 11:19.170 --> 11:22.980 So we've got bad attempt detected because we've got two. 11:23.010 --> 11:29.880 Now actually increasing this variable would not make sense because we just run this script once in the 11:29.880 --> 11:34.650 real world we're going to get this value from some other external storage. 11:34.680 --> 11:38.580 Now let me change that to three and see how this would behave. 11:38.820 --> 11:40.920 So we are blocked. 11:40.920 --> 11:48.960 But then we also kind of run some default code that detects the bad bunt attempt, you might want to 11:48.990 --> 11:52.110 log it someplace or do something else with it. 11:52.110 --> 11:57.570 But as I've said in this specific case, also default would make sense. 11:59.040 --> 12:00.570 So let's run it again. 12:02.610 --> 12:07.050 And if I change it to two back then this also works. 12:09.300 --> 12:12.600 Now finally you should know that into this switch statement. 12:12.600 --> 12:18.840 So the value that it gets evaluated you can put any expression doesn't have to be a variable. 12:18.870 --> 12:21.090 This is also a fine expression. 12:21.120 --> 12:24.240 Or you can have a function call if you prefer. 12:24.390 --> 12:27.720 And this also applies to the case instructions. 12:27.720 --> 12:35.220 Here you can also add an expression like for any reason you can check for that case that's different 12:35.220 --> 12:38.340 from languages like C or Java for example. 12:38.910 --> 12:42.180 But I think it's just useful to know now. 12:42.180 --> 12:43.050 All in all. 12:43.230 --> 12:50.040 To summarize, I think that you should just watch out with using the switch statement like this. 12:50.040 --> 12:59.250 So using it as a kind of a fallback structure where you want some code to be run always and then in 12:59.250 --> 13:08.670 some special cases also add some additional statements, because I just believe that this behavior of 13:08.670 --> 13:12.480 the switch statement is just not widely understood. 13:12.480 --> 13:18.930 And you also might hear that that's a bad practice not to use the break statements. 13:18.930 --> 13:22.440 So that's why I called this a little bit controversial. 13:22.440 --> 13:25.500 I think it's fine if the language allows that. 13:25.500 --> 13:27.780 But just be warned. 13:27.810 --> 13:36.660 That's just something that not everyone understands perfectly, and sometimes it just might be a good 13:36.660 --> 13:39.360 practice to avoid writing code. 13:39.360 --> 13:42.630 That is quite possible. 13:42.660 --> 13:45.510 Other people won't understand.