WEBVTT 00:00.390 --> 00:05.940 In this lecture I want to go over a different control flow structure that's able to make decisions. 00:06.080 --> 00:08.770 The switch statement. 00:08.930 --> 00:12.740 So here's how we make a switch statement. 00:12.730 --> 00:22.500 You start with surprise surprise the word switch is a key word in C++ and we have in here the parentheses 00:24.000 --> 00:33.470 urgency expression for now and this expression is what gets evaluated so much like the if statement. 00:33.470 --> 00:38.350 This is kind of the condition but it's a bit slightly different. 00:38.360 --> 00:40.270 You'll see why. 00:40.370 --> 00:45.990 So the next thing we have is something called a case. 00:46.040 --> 00:49.850 So these are all the different cases that can happen. 00:50.380 --> 00:57.980 And the cases are based on some constant expression. 00:58.370 --> 01:08.640 And again you'll see an example preceding and between this after the semi or this colon here we'll have 01:08.640 --> 01:13.800 all our statements like before statements go here. 01:13.840 --> 01:14.040 DE 01:17.550 --> 01:26.460 and optionally have something called a poor make statement as is optional and I'm not going to go over 01:26.460 --> 01:27.190 this quite yet. 01:27.200 --> 01:28.060 But ules. 01:28.080 --> 01:31.650 You'll see in a second what this is for. 01:31.710 --> 01:41.820 So you can have more Case statements Onsen expression say two and you can have as many as you want. 01:45.100 --> 01:46.600 OK statements 01:51.650 --> 01:57.880 in this last thing is kind of like the L's case in our IF statement last time. 01:58.280 --> 02:00.560 But we're going to call it the default. 02:00.560 --> 02:04.870 And this is the catch all for this switch statement. 02:05.330 --> 02:15.000 So if if somehow the expression didn't match one of these cases it would go to the default and do and 02:15.000 --> 02:16.550 do this. 02:16.860 --> 02:27.240 This set of code default statements. 02:27.290 --> 02:30.240 So again there's lots to unpack here. 02:30.470 --> 02:33.950 So the expression here Mohs. 02:34.190 --> 02:38.940 So this must evaluate to an integral type. 02:39.080 --> 02:45.320 So an integral type could be something like an int or could be a char. 02:45.320 --> 02:55.190 This is also an integral type or it could be a boolean that's also considered a integral type. 02:55.660 --> 03:07.380 So it has to evaluate to some something like an int or a char or a can for our purposes and here let's 03:07.380 --> 03:20.190 say let's say we use just X and we said indexical 0 K and the constant expressions here. 03:20.210 --> 03:22.880 This is just some constant value. 03:22.880 --> 03:29.780 So say let's say in constant 0 here. 03:30.410 --> 03:32.690 This is a constant expression as well. 03:32.690 --> 03:36.380 0 is just constant expression. 03:36.380 --> 03:41.350 Or here we can have one let's say. 03:41.720 --> 03:43.820 And that's also a constant expression. 03:45.310 --> 03:48.970 So let's just see a little example of this. 03:49.000 --> 03:51.260 Let's see Ouch. 03:51.310 --> 03:52.650 Case 0 03:57.110 --> 03:59.250 in C H. 04:01.910 --> 04:03.910 Case 1. 04:07.040 --> 04:14.200 And here in the default we will see a c h you fault's case 04:18.740 --> 04:22.280 this and that's right. 04:22.340 --> 04:26.810 You don't need these right now. 04:27.140 --> 04:28.160 And through this 04:36.500 --> 04:39.090 their case zero. 04:39.560 --> 04:43.500 So we assign X the value. 04:44.030 --> 04:51.230 And it's a switch on X and then it'll match this constant expression. 04:52.210 --> 04:59.290 Whatever it is say X is 1 Greenwich it did Case 1. 04:59.330 --> 05:00.760 Is this right here. 05:00.770 --> 05:09.450 So one is matched to this case 1 and then it did these these statements. 05:09.610 --> 05:20.300 Let's say do many geese one is d and s. 05:21.450 --> 05:23.130 To say 05:28.430 --> 05:38.710 right in this case one with the exclamation and just ones to gain so many statements. 05:38.710 --> 05:44.240 So what this break here though this is kind of weird right. 05:44.530 --> 05:50.400 Well this break will effectively just break out of the switch statement. 05:50.590 --> 05:54.220 Once it's once you get to this point. 05:54.250 --> 05:56.050 So it did give us one. 05:56.050 --> 05:59.460 And then it said case two or so he said. 05:59.470 --> 06:08.490 Case one in in case one statement two and then it hit this break point or is not breakpoint but break 06:08.490 --> 06:09.220 state. 06:09.470 --> 06:10.460 Right. 06:10.770 --> 06:19.480 And then it broke out of the switch entirely and came here to line let's say 39. 06:19.510 --> 06:41.490 So let's just say out of switch statement. 06:41.930 --> 06:45.950 So case one case one statement two. 06:46.190 --> 06:53.390 And then out of switch statement so it skipped say this default case. 06:53.810 --> 06:56.710 So let's see what happens if we didn't have this break. 07:01.140 --> 07:08.510 So it says case one case one statement two and then defaults case and then you're out of the switch 07:08.540 --> 07:09.330 statement. 07:09.780 --> 07:14.950 So like I said before it all go. 07:15.080 --> 07:18.510 So it'll switch on x. 07:18.540 --> 07:26.960 It'll find the first case that matches X and then it'll do every case below this one. 07:26.970 --> 07:39.450 So will do every case below case 1 until the end or until it hits a break and then it'll exit the switch. 07:39.450 --> 07:49.350 So this is a little bit different than if and else if control structure that we did last time. 07:49.960 --> 07:51.580 So that's why we need the break. 07:51.580 --> 08:01.120 So you'll usually see break for each case because usually we don't want to do cases below the case that 08:01.120 --> 08:02.260 we matched. 08:02.350 --> 08:06.920 Usually sometimes you do but usually do we don't. 08:06.970 --> 08:13.180 So one interesting thing about switch statements is you can't do something like this. 08:13.300 --> 08:22.530 Y equals zero. 08:22.750 --> 08:24.030 Run this. 08:24.190 --> 08:27.360 So air exists it's pointing to this. 08:27.400 --> 08:29.380 Why doesn't. 08:29.530 --> 08:31.100 It doesn't like this for some reason. 08:31.390 --> 08:43.150 So if you want to make new variables inside of a case you have to do this you have to use the braces 08:43.150 --> 08:44.930 that you talked about earlier. 08:46.310 --> 08:52.050 So just brace around the case say it why 0 08:55.480 --> 08:58.020 then this should work. 09:03.570 --> 09:04.230 Like that. 09:04.550 --> 09:06.500 So it doesn't mind it now. 09:06.890 --> 09:14.450 So just remember if you ever want to make new variables inside of a case for a switch state and always 09:14.450 --> 09:21.450 just wrap it around these curly braces. 09:21.500 --> 09:29.630 In fact what I usually do for switch statements in and generals I always make curly braces for the case 09:29.720 --> 09:31.520 every time. 09:33.160 --> 09:37.820 And that is I just wrap until the break and then that's it. 09:37.890 --> 09:47.520 This and that's usually how I write my switch statements. 09:47.680 --> 09:53.140 So let's see a real example of this. 09:53.250 --> 10:08.710 So it's delete lead on this. 10:08.770 --> 10:19.930 So let's solve the please enter day of the week from 1 to seven problem that you solved in the first 10:19.930 --> 10:20.420 section. 10:20.440 --> 10:35.300 So let's have a day equals zero saying ouch E's teacher day. 10:38.540 --> 10:39.560 6:59 10:45.850 --> 10:55.820 see in a and then three switch statement switch on the day. 10:56.050 --> 11:03.010 Case on remember we start the day on Monday right. 11:03.060 --> 11:05.410 So one is Monday. 11:05.510 --> 11:06.580 See out 11:10.150 --> 11:10.830 Monday. 11:11.810 --> 11:19.880 I'm not going to rate the braces for this like that and break it. 11:19.940 --> 11:21.950 We don't want it to fall through. 11:21.950 --> 11:35.530 If it was Monday or you don't want to do the cases below case 1 if it was Monday case to see Ouch Tuesday 11:38.260 --> 11:43.090 and all of the break. 11:43.380 --> 11:44.400 Case 3 11:47.570 --> 11:48.010 CH 11:51.020 --> 11:51.660 Wednesday 11:56.500 --> 11:56.630 the 12:01.210 --> 12:02.710 case for 12:06.000 --> 12:06.840 Thursday 12:20.440 --> 12:21.280 5 12:26.800 --> 12:27.490 Friday 12:35.290 --> 12:36.340 six 12:42.070 --> 12:42.850 Saturday 12:53.490 --> 12:56.660 seven C.. 12:56.750 --> 12:59.370 CH Sunday 13:02.660 --> 13:06.740 and remember we had the default case B 13:09.770 --> 13:21.210 say entered something outside of 6:59 say that was not such a valid day. 13:28.800 --> 13:30.420 Spell it wrong. 13:32.330 --> 13:45.310 Ballasted and through this so please enter day of the week so say 6 so it's Saturday. 13:45.540 --> 13:47.560 You should read this again. 13:47.670 --> 13:49.710 So we said negative one. 13:49.960 --> 13:54.360 That wasn't about day so it went to the default case. 13:54.530 --> 14:04.670 In this case the negative one is so see if we did three or remove all the breaks 14:08.210 --> 14:11.370 all the breaks from the tires which state and see what happens. 14:17.710 --> 14:20.140 So let's say it's Tuesday. 14:20.440 --> 14:25.900 So the day of the week is Tuesday Wednesday Thursday Friday Saturday Sunday and that was not a valid 14:25.900 --> 14:26.520 day. 14:26.950 --> 14:32.130 So see how it might fail through. 14:32.270 --> 14:36.770 So it matched to two notice it didn't match to one at all. 14:36.770 --> 14:39.390 There's no Monday being out put it here. 14:39.620 --> 14:44.140 So it it to and then it did every case below 2. 14:44.630 --> 14:48.950 So that is why you need the break statements 14:52.890 --> 14:57.890 so always remember that. 14:57.940 --> 15:03.410 So in the next lecture I'll show you even one more way of making decisions.