WEBVTT 0 00:00.670 --> 00:09.330 In this video we will learn about logical operators. logical operators are useful for writing compound conditional 1 00:09.330 --> 00:14.760 statements so already in the previous video we have learned about conditional statements, conditions we 2 00:14.760 --> 00:20.460 can define some condition for writing conditional statement we use a relational operator that is less 3 00:20.460 --> 00:25.770 than data than, not equal to for whatever the operator finds we can use these operators for writing the 4 00:25.770 --> 00:29.780 condition so we have written some program in the previous video. 5 00:29.880 --> 00:32.310 Now if I have more than one conditions. 6 00:32.340 --> 00:39.270 How to join them suppose i have two conditions that is X is less than y as well as I have 7 00:39.270 --> 00:41.680 one more condition that is X is less than Z. 8 00:41.860 --> 00:46.530 So x y z are some variables I want to combine these two conditions. 9 00:46.680 --> 00:48.260 What is the method of combining them. 10 00:48.270 --> 00:52.430 So if I combine then that will be called as compound conditional statement. 11 00:52.560 --> 00:59.920 So that compound conditional statement can be form using logical operators that are AND OR and NOT 12 01:00.110 --> 01:04.920 is used for negating the statement means if it is true then it will become false or vice versa 13 01:04.920 --> 01:10.830 AND, OR are used for making a compound conditional statement. 14 01:10.830 --> 01:13.500 So these operations are interesting. 15 01:13.800 --> 01:23.310 These are logical for AND in C++ symbol is && and OR it is || you will find it on keyboard 16 01:23.310 --> 01:26.030 find it on the keyboard somewhere near in enter key. 17 01:26.060 --> 01:29.730 You will find this, you have to hold shift for this one so there is a pipe. 18 01:29.730 --> 01:33.320 So these are the operators for AND OR. 19 01:33.930 --> 01:35.280 Now how they work. 20 01:35.370 --> 01:37.500 If I use AND how it works. 21 01:37.530 --> 01:38.860 See it is logical. 22 01:38.910 --> 01:45.610 So that depends upon its truth values so that we will see using a truth table. 23 01:46.200 --> 01:50.830 So first let us look at AND if I take an example from daily life. 24 01:50.860 --> 01:51.930 See when we talk. 25 01:52.030 --> 01:54.920 we use this word and for joining. 26 01:54.920 --> 01:57.090 Two sentences right. 27 01:57.270 --> 02:00.190 So what is the meaning of that and. 28 02:00.330 --> 02:05.400 even though we are joining two statements or sentences but and place what roll. 29 02:05.580 --> 02:07.430 So let us observe that clearly. 30 02:07.890 --> 02:11.510 So I take one example through that I will explain you what does it mean by 31 02:11.580 --> 02:21.080 And. see if I say that I'm wearing black t shirt and a cap. 32 02:22.480 --> 02:24.650 So I have combined two statements. 33 02:24.790 --> 02:31.480 So let me elaborate once again I'm wearing black t shirt and I am wearing a cap. 34 02:31.810 --> 02:34.240 So those statements are that I have joined them. 35 02:34.390 --> 02:38.250 And so now you tell me what I said just now. 36 02:38.260 --> 02:39.550 Is it true. 37 02:39.550 --> 02:40.860 Is it true. 38 02:40.900 --> 02:42.210 Let us check it. 39 02:42.360 --> 02:45.020 t-shirt this is 1st statement. 40 02:45.070 --> 02:51.210 I'm not writing a full sentence, I'm wearing t shirt then Next one is I'm wearing cap. 41 02:51.240 --> 02:53.780 Now these two are two different sentences right. 42 02:53.920 --> 03:02.860 Next I will combine these two by using and so t-shirt is one statement and I will write that word 43 03:02.890 --> 03:10.510 and instead of using operator so that in C++ you have to use operators but then this is gap. 44 03:10.530 --> 03:19.160 Now I have two statements these two statements, now look at this I'm wearing t shirt, true. 45 03:19.520 --> 03:23.430 Suppose I'm wearing cap then also true 46 03:23.520 --> 03:31.960 Then if I say I'm wearing a t shirt and am wearing cap will the complete statement be true or false 47 03:32.440 --> 03:33.080 it will be true. 48 03:33.100 --> 03:35.270 If I'm wearing a cap it's true. 49 03:37.330 --> 03:39.780 Second one I'm wearing t shirt. 50 03:39.940 --> 03:42.970 Yes but I'm not wearing cap false. 51 03:43.660 --> 03:49.930 If I say I'm wearing cap if you see I'm not wearing cap which is false so t shirt is true but cap is false 52 03:49.950 --> 03:51.550 so not complete statement. 53 03:51.550 --> 03:58.780 I'm waiting t shirt and I'm wearing cap so the complete sentences is wrong it's false so this will be 54 03:58.780 --> 04:00.250 false. 55 04:00.790 --> 04:03.870 The next one I'm wearing t shirt. 56 04:03.940 --> 04:08.920 suppose i'm not wearing t shirt I'm wearing some other thing like a blazer or shirt then my statement will 57 04:08.920 --> 04:09.970 be false. 58 04:10.160 --> 04:12.160 I suppose I'm reading cap. 59 04:12.700 --> 04:15.140 If you find me I'm reading cap now. 60 04:15.640 --> 04:22.540 If I say that I'm wearing t shirt and I'm wearing cap so one off my sentence is true. 61 04:22.600 --> 04:23.170 Which one. 62 04:23.170 --> 04:25.690 The cap one is true but the t shirt one is false. 63 04:25.690 --> 04:31.790 So in that way the complete sentence is false though one of them is true but the other one is false 64 04:31.790 --> 04:33.310 so the complete statement is false. 65 04:33.340 --> 04:34.970 So this would be false. 66 04:34.990 --> 04:41.170 Then last one I'm not wearing t shirt even I'm not wearing cap but I am saying that I'm wearing t shirt 67 04:41.250 --> 04:42.640 and I'm wearing cap. 68 04:42.700 --> 04:43.810 Both are false. 69 04:43.840 --> 04:45.880 So then also my statement is false. 70 04:47.650 --> 04:52.410 This is the truth table it is called as a truth table. 71 04:52.990 --> 04:59.050 So truth table for AND for AND operation I have written and here. 72 04:59.170 --> 05:00.610 So this is truth table for that. 73 05:01.090 --> 05:08.290 So now we can understand when AND will be true if both those statements are true then only it will 74 05:08.290 --> 05:14.610 be true if any one this statement is false then the result of and is false so for preparing 75 05:14.700 --> 05:18.060 both conditional statements when you are joining these two. 76 05:18.230 --> 05:23.860 And if you are writing and in between them then if this is a true one this is also true. 77 05:23.860 --> 05:29.530 then only the entire statement will be true if any one of the statement is false then the resultof 78 05:29.620 --> 05:31.170 and is false. 79 05:31.210 --> 05:33.580 So this is true but this is false If suppose. 80 05:33.580 --> 05:40.930 Then the result is false. this logical operation works on boolean value so that is true and false only 81 05:41.110 --> 05:46.780 right and the result is again true or false they should be very much clear for you right. now, 82 05:46.840 --> 05:48.750 Next we will see OR operation. 83 05:48.760 --> 05:54.130 So for OR operation I will use these two only and I will just change this one I remove this and 84 05:54.130 --> 05:57.430 I'll make a table for OR. yes it's ready for or now. 85 05:57.430 --> 06:03.700 Now I have two statement I'm wearing t shirt I'm wearing cap next let me read it out. 86 06:04.240 --> 06:07.980 I'm wearing t shirt or I'm wearing gap. 87 06:08.140 --> 06:14.440 These are two statements I have them with or, or means either this or that. 88 06:14.600 --> 06:18.330 yes the word or now gives the clear meaning right. 89 06:18.460 --> 06:22.210 This or that, AND this also and that also. 90 06:22.500 --> 06:25.110 Both, but or means this or that. 91 06:25.180 --> 06:25.650 Right. 92 06:25.720 --> 06:27.150 So let us see how it works. 93 06:27.160 --> 06:32.200 So I will take these examples and show you if both the statements are true. 94 06:32.200 --> 06:35.770 Suppose I'm getting a cap so I'm wearing a t shirt true. 95 06:36.160 --> 06:37.510 I'm wearing cap too. 96 06:37.510 --> 06:38.230 Both are true. 97 06:38.230 --> 06:39.400 So my statement is true. 98 06:39.520 --> 06:41.840 Yes this is true. 99 06:41.840 --> 06:43.970 Now second one I'm wearing a t shirt. 100 06:43.990 --> 06:50.460 Yes I'm getting t shirt true that I'm wearing cap I'm not wearing cap it's false it's false. 101 06:50.470 --> 06:52.240 Now let me complete the statement. 102 06:52.240 --> 06:56.280 I'm wearing t shirt or I'm wearing cap so or means. 103 06:56.290 --> 06:58.600 This one is true right t shirt is true. 104 06:59.230 --> 07:00.630 So this is true. 105 07:01.210 --> 07:05.770 So in case of or this is true now let us come to the second one next one. 106 07:05.780 --> 07:07.640 third one see false. 107 07:07.720 --> 07:08.910 I'm not wearing T-shirts suppose. 108 07:09.130 --> 07:10.210 But I'm wearing cap. 109 07:10.330 --> 07:17.290 So if I tell the statement that I'm wearing t shirt or I'm wearing cap so if I'm not wearing t shirt 110 07:17.320 --> 07:20.480 but I'm getting cap then my statement is true because they said OR. 111 07:20.890 --> 07:23.980 So this is true next. 112 07:23.980 --> 07:24.630 Last one. 113 07:24.670 --> 07:25.510 What are false. 114 07:25.510 --> 07:30.820 I'm neither wearing t shirt nor wearing a cap but I am sayingthat I'm wearing t shirt or am wearing 115 07:30.820 --> 07:31.180 cap. 116 07:31.540 --> 07:32.880 So none of them is true. 117 07:32.920 --> 07:40.210 Suppose none of them is true then this is false this is the truth table for or. 118 07:40.300 --> 07:46.310 How to remember this one if any one of them is a true it will be true this is true so it is true this 119 07:46.310 --> 07:46.770 is true. 120 07:46.790 --> 07:55.790 So this is true both are false then false so the difference between AND and OR is in and if one is 121 07:55.790 --> 07:57.800 false everything is false. 122 07:59.320 --> 08:02.000 In or if one is true everything is true. 123 08:02.320 --> 08:10.360 this way you can remember it so it means in this one if I write OR right in C++ programming if i write or if this is 124 08:10.360 --> 08:13.750 true and this is false then also that is true. 125 08:14.260 --> 08:16.100 And even if this is false. 126 08:16.220 --> 08:21.350 And this is true then also those are true if both are true theen also that is true and when 127 08:21.350 --> 08:25.840 it could be false if both the conditions are false then it will be false. 128 08:25.870 --> 08:32.230 So this is how logical operators are useful for combining conditions mostly students get confused here in 129 08:32.230 --> 08:32.890 the beginning. 130 08:33.040 --> 08:40.090 That right two conditions they write a comma or they leave blank no conditional statement, two conditional statement 131 08:40.090 --> 08:44.940 using relational operators that are joint using logical operators. 132 08:45.270 --> 08:50.620 Then one last thing I have to show you that is NOT so I'll just remove this table and I show you not 133 08:51.560 --> 08:58.300 so the last operator that is not not is used for negating a statement negating means if it is true it will 134 08:58.300 --> 09:00.580 become false if it is false it will become true. 135 09:00.610 --> 09:07.700 So if suppose I'm wearing t shirt if it is true then not of that one means not I'm wearing t shirts. 136 09:07.720 --> 09:10.070 So really I'm wearing a t shirt right. 137 09:10.080 --> 09:12.500 True but not means it is false. 138 09:12.550 --> 09:15.950 Not getting t shirt so it is false. 139 09:16.000 --> 09:25.310 Next I'm wearing t shirt, suppose false I'm not wearing t shirt but I said that I'm wearing t shirt I'm 140 09:25.320 --> 09:30.060 wearing t shirt now if you make not off that statement means not wearing. 141 09:30.060 --> 09:30.660 That is true. 142 09:30.840 --> 09:33.130 So it will be true. 143 09:33.210 --> 09:38.310 So if your statement is a true then the negation will become false and if it is a false then the negation 144 09:38.310 --> 09:39.740 will become true. 145 09:39.750 --> 09:41.040 This is very useful. 146 09:41.040 --> 09:46.910 So it looks simple and right now it may look useless but it is very useful. where it is useful. 147 09:46.920 --> 09:49.330 I'm show you in some other topic. 148 09:49.710 --> 09:52.660 So that's all about these logical operators. 149 09:52.740 --> 09:56.310 These are used for writing compound conditional statement. 150 09:56.310 --> 10:00.840 We will see how to use them in the next video I will write a program and show you.