WEBVTT 00:00.530 --> 00:06.550 He went over some boolean logic rules last time but we haven't learned what it means in C++ yet. 00:06.980 --> 00:11.970 So to create a million variable we write them like this. 00:11.970 --> 00:15.350 So we say pool just short for Boullion. 00:15.350 --> 00:21.910 That's the type in which you give it the identifiers of hooly in my boolean 00:27.430 --> 00:35.530 in course who's only have two values and they are of course true. 00:36.900 --> 00:49.370 Or False and True or false are also keywords in C++ say true or false both keywords. 00:51.490 --> 00:56.730 So there are also other operators that can evaluate to TRUE and FALSE. 00:56.920 --> 01:08.930 The greater than sign less than sign and e greater than or equal to sign and the less than or equal 01:09.110 --> 01:15.460 sign all of these will produce a true or false value. 01:15.460 --> 01:17.520 So let's look an example. 01:17.540 --> 01:24.060 Samian bhool results in 10 is greater than 3. 01:24.220 --> 01:26.650 So this of course this is true. 01:26.680 --> 01:27.330 Right. 01:27.700 --> 01:34.680 So you can even put this out alue So it's 01:38.010 --> 01:41.250 as it's. 01:41.380 --> 01:41.740 It's 01:49.850 --> 01:52.160 an see what happens. 01:52.960 --> 01:55.750 So your result is 1. 01:55.780 --> 01:57.270 So why is that. 01:57.310 --> 02:10.690 Well booleans internally are represented by numbers so true here is represented by 1 and FALSE is represented 02:10.750 --> 02:14.010 by 0. 02:14.070 --> 02:17.990 In fact True's not actually are by one but that's the output. 02:17.990 --> 02:21.680 It'll have to is really anything. 02:24.090 --> 02:37.600 Except zero actually any number the size 0 is considered true in terms of boolean logic. 02:37.680 --> 02:47.080 So there's also another operator that can evaluate to TRUE and FALSE which is the quality. 02:47.080 --> 02:55.020 Operator So which is defined as two equal signs. 02:55.110 --> 03:05.790 A lot of students will get this confused with the assignment operator as they both use equal signs and 03:05.790 --> 03:14.980 just remember that if you're testing for equality you always want to use two equal science one equal 03:14.980 --> 03:18.430 sign means assignment. 03:18.490 --> 03:24.410 This means compare two or equals two. 03:25.230 --> 03:29.240 Lot of students will get this mixed up and I certainly did. 03:29.350 --> 03:33.230 I started at so. 03:33.230 --> 03:41.710 Also keep in mind as well that it's comparing to floating point numbers. 03:42.530 --> 03:45.990 It's with the equality sign is usually a bad idea. 03:46.000 --> 03:48.940 And let's see why that is. 03:49.540 --> 03:59.170 So safe float pie and fruit pie to say because it has two more values to it. 04:01.010 --> 04:07.810 So let's compare PI with PI to and see what the result. 04:07.840 --> 04:11.380 It's it's two. 04:11.530 --> 04:12.730 It's this 04:20.130 --> 04:21.130 in. 04:21.230 --> 04:22.160 So there you go. 04:22.160 --> 04:33.020 So their results is zero or false because the precision of pi 2 is not the same as the precision of 04:33.530 --> 04:36.250 the first pi. 04:36.260 --> 04:41.260 So if I said PI twos you put 1 4 and are in it again. 04:41.540 --> 04:51.060 This is true but usually you'll see that floating point numbers are basically never the same. 04:51.150 --> 04:59.520 You never really want to compare them as quality Neverland duty quality operation on two floats because 05:00.060 --> 05:02.570 typically this will never be true. 05:03.470 --> 05:08.950 But we will see later on how we can possibly fix this. 05:09.050 --> 05:20.610 But for now just know that just don't compare to floating point numbers with a quality. 05:20.640 --> 05:24.740 The other operator we can use. 05:24.740 --> 05:29.910 Here is the inverse operator. 05:30.050 --> 05:31.900 So let's say we had results. 05:32.060 --> 05:41.610 Is Well it's actually called the not operator which is exclamation point to result. 05:41.610 --> 05:44.580 So before we said this is false. 05:44.600 --> 05:47.040 So these are not the same right. 05:47.610 --> 05:55.200 But if we say result equals two not the result then it'll change whatever the value. 05:55.200 --> 05:59.310 So let's try it again and we see 06:05.840 --> 06:16.670 and we see that the result is 1 because it's switch or negated the false into a true. 06:16.870 --> 06:19.100 So the opposite of false is true. 06:24.250 --> 06:36.320 So there was actually another version of equality that we can use and it has to do with the not operator 06:36.420 --> 06:41.110 in say not equal to this. 06:41.270 --> 06:47.110 This says not equal to pi is not equal to pi 2. 06:47.440 --> 06:48.960 So this should be true. 06:51.710 --> 06:52.170 OK. 06:52.220 --> 06:54.140 See. 06:54.220 --> 06:59.460 So it's kind of like the opposite of the equal to. 06:59.510 --> 07:04.530 Another way you can write this is say equal to here and then say not here. 07:04.630 --> 07:05.620 This is equivalent 07:08.740 --> 07:09.190 staff. 07:09.340 --> 07:09.850 Yeah. 07:12.830 --> 07:23.840 So the last two operators are what we covered last time which are the and logical and logical or. 07:23.840 --> 07:26.170 So let's get rid of this 07:29.810 --> 07:39.870 just right this one and let's say we had true. 07:40.100 --> 07:49.280 And so we have to ampersands to make the logical answer remember that logical and is always to ampersands 07:50.370 --> 07:54.640 and false is of course should be false. 07:54.640 --> 07:55.040 Right. 07:55.120 --> 07:56.500 So you're in this 08:01.880 --> 08:06.020 you're in this it's false. 08:06.160 --> 08:20.770 Ceara we want to do or say it or true or church two vertical bars. 08:20.910 --> 08:29.670 So we have to ampersands four and in two vertical bars four or so. 08:29.670 --> 08:33.710 True or false of course is true. 08:34.660 --> 08:36.590 We want to make this false. 08:36.590 --> 08:48.060 You say true or false or false horses false for some reason it never once printed out properly. 08:48.400 --> 08:51.530 So the value of result is false. 08:53.210 --> 08:59.300 So let's do a few examples and really try to solidify this a bit. 08:59.420 --> 09:00.830 Let's use 09:05.300 --> 09:24.120 that and say we hand who a equals true in Rule B is false in it's have some integers in each x 10 y 09:24.510 --> 09:28.990 z or and you will have results. 09:29.110 --> 09:35.200 Lool so it's is. 09:35.330 --> 09:46.190 So it's a and b or x is greater than Y. 09:46.220 --> 09:53.310 So what is the output of this do you think so. 09:53.800 --> 10:00.870 A is true and B which is false will be false. 10:01.000 --> 10:05.040 Cause for and both would have to be true. 10:05.040 --> 10:13.520 For this to evaluate to true or X which is 10 y is zero. 10:14.860 --> 10:17.580 So 10 of course is greater than zero. 10:18.010 --> 10:22.780 So false or true is true. 10:24.510 --> 10:27.870 See it right and we are. 10:27.870 --> 10:30.180 So all your result is true. 10:30.560 --> 10:34.380 One do another example 10:39.170 --> 10:40.210 soon. 10:40.410 --> 10:41.970 A not A 10:44.760 --> 10:48.050 or B and. 10:49.280 --> 10:56.370 X X X X less than or equal to y 10:59.100 --> 11:00.290 k. 11:00.420 --> 11:02.870 What would be the output here. 11:03.270 --> 11:05.160 Well a is true. 11:05.190 --> 11:21.430 So not a is false or false is totally false and X is 10 so x is not less than Y which is 0. 11:21.480 --> 11:25.400 So this would also be false and the whole thing should be false. 11:26.940 --> 11:32.280 So try and it's let's try one more 11:35.950 --> 11:46.550 let's say not and those are using parentheses for these parentheses really do come in handy in especially 11:46.550 --> 11:47.410 in boolean logic. 11:47.420 --> 11:52.000 But any kind of earth Medich operation so let's say 11:54.630 --> 11:57.630 next mission. 11:58.090 --> 12:02.160 Actually equal. 12:04.140 --> 12:04.890 Equal 12:07.980 --> 12:09.540 today. 12:09.640 --> 12:13.370 So what would be the results of this well. 12:14.430 --> 12:22.530 True is definitely not equal to false and X is definitely not equal to whine because X is 10 and Y's 12:22.550 --> 12:23.530 0. 12:23.880 --> 12:29.430 So the whole thing should be false but it should be negated at the end. 12:29.430 --> 12:32.410 Right and that's why we have these parentheses. 12:32.880 --> 12:34.850 And the whole thing should be true. 12:37.190 --> 12:38.050 And it is 12:41.800 --> 12:49.240 so in the next lecture we'll be using this to actually start making our decisions in our output is.