WEBVTT 00:01.020 --> 00:10.780 Last time I introduce types like int char and double and before you get into explaining more about types 00:11.060 --> 00:20.320 I did something in the last lecture I did this really 10 and three this is what's called the comment 00:20.950 --> 00:24.950 and you'll see a comment above here as well. 00:25.180 --> 00:35.150 The name of my seat BP file variables the anti-common is ignored by the compiler. 00:35.150 --> 00:40.820 It's really just a way to mark something for programmers so I thought. 00:41.240 --> 00:44.310 Just explain that. 00:44.400 --> 00:49.330 So no this gets compiled this is just for us. 00:49.370 --> 01:00.620 So in this lecture I want to talk about more types and a little bit of why we have types and how their 01:00.620 --> 01:02.560 sizes. 01:02.750 --> 01:12.990 So I'm sure you've heard of binary before the ones and zeros and a bit you may have heard before as 01:12.990 --> 01:13.600 well. 01:13.620 --> 01:21.900 And that contains either the value 1 or 0 which means it's base to number. 01:21.900 --> 01:31.420 So our typical number system is base 10 which goes from 0 to 0 to 9 right. 01:31.440 --> 01:34.720 In this in binary is either 0 or what. 01:38.990 --> 01:52.680 So if we had a base 10 numbers say 123 and we'd understand the base number like this one 01:55.160 --> 02:06.890 one times 10 to that is power power to was 02:09.220 --> 02:19.180 you times 10 to the power of one plus three 02:21.990 --> 02:23.630 times. 02:24.430 --> 02:27.940 Ten to the power of zero. 02:28.540 --> 02:35.210 So meaning this is the ones so tenth power of zero just ones of time series three. 02:35.560 --> 02:41.230 And then this would be the tens because it's one to the power one doesn't change change the tune at 02:41.240 --> 02:41.960 all. 02:42.130 --> 02:50.310 So just be two times 10 or 20 and then 10 to the power of two which would be 100 times one is hundred. 02:50.620 --> 02:54.740 So all that added together is 123. 02:54.740 --> 03:02.970 So but if we had a 4 bit number what's so one bit is either there or one. 03:03.250 --> 03:11.270 So but if we had a forbit number say like this what would that be. 03:11.270 --> 03:17.960 What is the Momi the base 10 representation of that number. 03:18.340 --> 03:22.280 So this is not too difficult to do. 03:22.660 --> 03:32.410 So you'd say 1 times 2 to the power of three right. 03:33.540 --> 03:33.680 Right. 03:33.940 --> 03:42.470 This because this would be a power of zero to the power one due to the power of two and two to the power 03:42.470 --> 03:49.540 of three races in the very last one or the very low left most one plus zero times. 03:52.030 --> 04:03.300 Tines to the power of two was zero times two power. 04:04.100 --> 04:13.530 One was one times two power zero. 04:14.940 --> 04:15.600 Right. 04:15.670 --> 04:23.630 And all of that is equal to let's say eight Ciro. 04:23.770 --> 04:24.990 Right. 04:25.030 --> 04:38.690 Zero us one and just nine this number 1 0 1 in binary is really just our nine. 04:39.450 --> 04:49.090 And this is an easy easy way to determine what is or how to actually make a 04:51.990 --> 05:02.800 translate let's say a binary number to a base 10 or so all of this is really just to say that 05:05.530 --> 05:17.910 if you want a well a byte that you may have heard of as well like a megabyte or kilobyte is really 8 05:18.030 --> 05:20.010 bits so two. 05:20.100 --> 05:28.570 So this is four bits and really we want a byte is 8 bits 05:32.240 --> 05:36.060 and all our types are actually measured in bytes. 05:36.070 --> 05:41.230 So how how big our types are is usually measured in bytes. 05:42.170 --> 05:53.700 So the size I said before completely system dependent actually and we can actually figure out what those 05:53.700 --> 06:00.470 sizes are if we use what's called the size of operator. 06:00.510 --> 06:05.440 So let's find out what the sizes of the types that we use last time are. 06:05.460 --> 06:20.640 So let's say see ouch and do the int size of an inch is and then we just say size of it. 06:25.650 --> 06:26.500 And we'll see. 06:26.510 --> 06:32.840 All our other types as well the size char is 06:48.230 --> 06:48.760 ch 07:00.420 --> 07:02.390 you look at double as well. 07:18.520 --> 07:20.410 So if we run this 07:26.000 --> 07:27.620 so we'll see. 07:27.620 --> 07:33.490 So like I said they're all measured in bytes so the size of an int is 4 bytes. 07:33.830 --> 07:42.570 So that's 32 bit and the size of a char interestingly is just one byte and float is the same as in it 07:42.570 --> 07:46.700 it's 4 bytes and double is double a float. 07:46.710 --> 07:48.090 So it's eight bytes. 07:50.670 --> 07:57.220 So because of their sizes types only have a certain value range they can be. 07:57.240 --> 08:00.690 So for example in in 08:05.720 --> 08:11.740 an integer which can have the values are in the positive zero or negative. 08:11.950 --> 08:13.010 Right. 08:13.710 --> 08:19.480 It can only have the values of negative to shew the power 08:21.950 --> 08:29.940 of 31 and it's 31 because 4 bytes is 32 bits. 08:29.940 --> 08:37.020 But since we have negative values it has to be divided by two which would knock off. 08:37.050 --> 08:42.460 So it should be 32 bits but since we have to divide what two we have to knock off one. 08:42.690 --> 08:46.570 So it's only 30 power 31. 08:46.830 --> 09:05.560 So it's you can go negative 2 to the power of 31 to 2 to the power of 31 minus 1 and it's minus 1 because 09:05.560 --> 09:09.110 of zero. 09:09.240 --> 09:11.360 You have to count zero as well. 09:11.610 --> 09:14.570 So it's always minus 1. 09:14.590 --> 09:19.610 So this is the main reason why we have different types or one of the main reasons. 09:19.840 --> 09:26.920 Because they are different sizes in the computer's memory and we can change the value ranges by adding 09:27.280 --> 09:29.740 what's called an unsigned 09:32.550 --> 09:42.600 unsigned keyword say unsigned int x is zero right. 09:42.610 --> 09:47.710 So unsigned means it can't be negative and must be positive. 09:48.710 --> 09:52.680 And unsigned also doesn't change the size of the type at all. 09:52.700 --> 10:08.170 It will only change the value range thus it will have the range from zero to two to power 30 to rate 10:08.200 --> 10:15.630 as it's 32 bits or bytes minus one because of zero. 10:15.660 --> 10:22.720 So this is now 30 to 32 instead of power 31. 10:22.760 --> 10:28.210 It was up here because we're completely eliminating all negative numbers 10:31.460 --> 10:38.870 so this is not the only reason why we have types in the language though. 10:38.990 --> 10:43.630 And note that int and float are the same size. 10:43.760 --> 10:45.150 But let's try. 10:45.170 --> 10:53.100 Let's try this let's get rid of unsigned So let's say we have an X or it's called something better. 10:53.250 --> 11:11.950 Now and float float in footwell won't give it 3.20 for a number and let's say we say interval equals 11:11.960 --> 11:13.220 to fluvial 11:17.950 --> 11:23.820 and then let's print out each value. 11:27.850 --> 11:30.720 Now is 11:39.140 --> 11:48.090 this not tell us. 11:48.260 --> 11:54.550 CH So see how the info is 3 right. 11:55.900 --> 12:03.490 It's not 3.1 4 this is because of how the computer will interpret the integers. 12:03.490 --> 12:06.780 Integers have to be whole number. 12:07.420 --> 12:21.120 But if we did something like bow equals six and then we kind of reverse this. 12:21.290 --> 12:24.780 Now here like that. 12:24.790 --> 12:31.530 And then we ran it. 12:32.440 --> 12:45.030 Well some compilers actually say 6.00 actually are actually no sorry since this actually my fault book 12:45.410 --> 12:47.840 is only a fluke. 12:48.480 --> 12:54.870 Sorry. 12:55.420 --> 12:57.040 So it classics. 12:57.160 --> 13:00.780 But some some will actually output six point 0. 13:01.240 --> 13:07.360 Instead Not just six. 13:07.470 --> 13:10.270 So it actually interprets completely differently. 13:12.550 --> 13:13.060 So 13:16.020 --> 13:22.560 remember that even if they're the same size different types are interpreted differently. 13:22.560 --> 13:31.350 The compiler often gives you some kind of warning or maybe even error sometimes if you just start assigning 13:31.350 --> 13:32.250 types. 13:32.250 --> 13:38.810 So here here we're assigning this into vowed to be the float for example. 13:38.850 --> 13:44.040 So if you just start assigning types without being careful and thinking about doing might end up with 13:44.040 --> 13:46.860 something you didn't want to happen. 13:47.660 --> 13:52.580 So in the next lecture we'll start talking about arithmetic operators operations.